Methods and apparatus for enhanced ion based sample detection using selective pre-separation and amplificaton

ABSTRACT

The invention relates generally to ion mobility based systems, methods and devices for analyzing samples and, more particularly, to sample pre-separation and amplification.

REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.11/015,413, filed Dec. 17, 2004, entitled “Methods and Apparatus forEnhanced Ion Based Sample Detection Using Selective Pre-Separation andAmplification”; and claims the benefit of and priority to: U.S.Provisional Application No. 60/531,480, filed on Dec. 18, 2003, entitled“Pre-Separation for Matrix Compounds for Analysis, Filtering, orDetection”; U.S. Provisional Application No. 60/533,676, filed on Dec.31, 2003, entitled “Pre-Separation for Matrix Compounds for Analysis,Filtering, or Detection”; and U.S. Provisional Application No.60/556,414, filed on Mar. 25, 2004, entitled “Chemical AmplificationSystem for DMS.” The entire teachings of the above referencedapplications are incorporated herein by reference.

This application also incorporates by reference the entire contents ofthe following co-pending U.S. patent applications: U.S. Ser. No.10/187,464, filed on 28 Jun. 2002; U.S. Ser. No. 10/215,251, filed on 7Aug. 2002; U.S. Ser. No. 10/462,206, filed on 13 Jun. 2003; U.S. Ser.No. 10/684,332, filed on 10 Oct. 2003; U.S. Ser. No. 10/734,499, filedon 12 Dec. 2003; U.S. Ser. No. 10/738,967, filed on 17 Dec. 2003; U.S.Ser. No. 10/797,466, filed on 10 Mar. 2004; U.S. Ser. No. 10/821,812,filed on 8 Apr. 2004; U.S. Ser. No. 10/824,674, filed on 14 Apr. 2004;U.S. Ser. No. 10/836,432, filed on 30 Apr. 2004; U.S. Ser. No.10/840,829, filed on 7 May 2004; U.S. Ser. No. 10/866,645, filed on 10Jun. 2004; U.S. Ser. No. 10/887,016, filed on 8 Jul. 2004; U.S. Ser. No.10/894,861, filed on 19 Jul. 2004; U.S. Ser. No. 10/903,497, filed on 30Jul. 2004; U.S. Ser. No. 10/916,249, filed on 10 Aug. 2004; U.S. Ser.No. 10/932,986, filed on 2 Sep. 2004; U.S. Ser. No. 10/943,523, filed on17 Sep. 2004; U.S. Ser. No. 10/981,001, filed on 4 Nov. 2004; and U.S.Ser. No. 10/998,344, filed 24 Nov. 2004.

FIELD OF THE INVENTION

The invention relates generally to mobility-based systems, methods anddevices for analyzing samples. More particularly, in variousembodiments, the invention relates to improving the detection capabilityof ion mobility based systems using pre-separation and amplification ofselected ion species of a sample.

BACKGROUND

There are a number of different circumstances in which it is desirableto perform analysis to identify compounds in a sample. Such samples maybe taken directly from the environment or they may be provided by frontend specialized devices to separate or prepare compounds beforeanalysis. There exists, a demand for low cost, compact, low-power,accurate, easy to use, and reliable devices capable of detectingcompounds in a sample.

One class of known analyzers are mass spectrometers (MS). Massspectrometers are generally recognized as being the most accurate typeof analyzers for compound identification. However, mass spectrometersare quite expensive, easily exceeding a cost of $100,000 or more and arephysically large enough to become difficult to deploy everywhere thepublic might be exposed to dangerous chemicals. Mass spectrometers alsosuffer from other shortcomings such as the need to operate at relativelylow pressures, resulting in complex support systems. They also need ahighly trained operator to tend to and interpret the results.Accordingly, mass spectrometers are generally difficult to use outsideof laboratories.

A class of chemical analysis instruments more suitable for fieldoperation is known as Field Asymmetric Ion Mobility Spectrometers(FAIMS) or Differential Mobility Spectrometers (DMS), and also known asRadio Frequency Ion Mobility Spectrometers (RFIMS) among other names.Hereinafter, FAIMS, DMS, and RFIMS, are referred to collectively as DMS.This type of spectrometer subjects an ionized fluid (e.g., gas, liquidor vaper) sample to a varying high-low asymmetric electric field andfilters ions based on their field mobility.

The sample flows through a filter field which allows selected ionspecies to pass through, according to a compensation voltage (Vcomp)applied to filter electrodes, and specifically those ions that exhibitparticular mobility responses to the filter field. An ion detector thencollects ion intensity/abundancy data for the detected ions. Theintensity data exhibits attributes, such as “peaks” at particularcompensation voltages.

A typical DMS device includes a pair of electrodes in a drift tube. Anasymmetric RF field is applied to the electrodes across the ion flowpath. The asymmetric RF field, as shown in FIG. 1, alternates between ahigh or “peak” field strength and a low field strength. The field variesover a particular time period (T), frequency (f) and duty cycle (d). Thefield strength E varies with an applied field voltage (Vrf) and the sizeof the gap between the electrodes. Ions pass through the gap between theelectrodes when their net transverse displacement per period of theasymmetric field is zero. In contrast, ions that undergo a netdisplacement eventually undergo collisional neutralization on one of theelectrodes. In a given RF field, a displaced ion can be restored to thecenter of the gap (i.e. compensated, with no net displacement for thation) by superimposing a low strength direct current (dc) electric field(e.g., by applying Vcomp across the filter electrodes) on the RF. Ionswith differing displacement (owing to characteristic dependence ofmobility in the particular field) pass through the gap at differingcharacteristic compensation voltages. By applying a substantiallyconstant Vcomp, the system can be made to function as a continuous ionfilter. Alternatively, scanning Vcomp obtains a spectral measurement fora sample. A recorded image of the spectral scan of the sample issometimes referred to as a “mobility scan” or as an “ionogram.”

Examples of mobility scans based on the output from a DMS device areshown in FIGS. 2A and 2B. The compounds for which scans are depicted areacetone and an isomer of xylene (o-xylene). The scan of FIG. 2A resultedfrom a single compound, acetone, being independently applied to the DMSanalyzer. The illustrated plot is typical of the observed response ofthe DMS device, with an intensity of detected ions dependent on Vcomp.For example, the acetone sample exhibits a peak intensity response at aVcomp of approximately −2 Vdc.

FIG. 2B illustrates the results when analyzing a mixture of acetone ando-xylene. The combined response shows two peaks in approximately thesame region as for the independent case. The compounds in the mixturecan be detected by comparing the response against a library, forexample, of stored known responses for independently analyzed compounds,or libraries of mixtures. Thus, the scans for independently analyzedcompounds, such as the scan of FIG. 2A for acetone, can be stored in acomputer system, and when compound responses such as that in FIG. 2B areobserved, the relative locations of the peaks can be compared againstthe stored responses in the library to determine the constitution of thecompound.

A specific RF field voltage and field compensation voltage Vcomp permitsonly ion species having a particular ion mobility characteristic to passthrough the filter to the detector. By noting the RF level andcompensation voltage and the corresponding detected signal, various ionspecies can be identified, as well as their relative concentrations (asseen in the peak characteristics).

Consider a plot of ion mobility dependence on Vrf, as shown in FIG. 3.This figure shows ion intensity/abundancy versus RF field strength forthree examples of ions, with field dependent mobility (expressed as thecoefficient of high field mobility, α) shown for species at greater,equal to and less than zero. The velocity of an ion can be measured inan electric field (E) low enough so that velocity (v) is proportional tothe electrical field as v=KE, through a coefficient (K) called thecoefficient of mobility. K can be shown to be related to the ion speciesand gas molecular interaction properties. This coefficient of mobilityis considered to be a unique parameter that enables the identificationof different ion species and is determined by, ion properties such ascharge, size, and mass as well as the collision frequency and energyobtained by ions between collisions.

When the ratio of E/N, where N is gas density, is small, K is constantin value, but at increasing E/N values, the coefficient of mobilitybegins to vary. The effect of the electric field can be expressedapproximately as K(E)=K(0)[1+α(E)], where K(0) is a low voltagecoefficient of mobility, and α is a specific parameter showing theelectric field dependence of mobility for a specific ion.

Thus, as shown in FIG. 3, at relatively low electric field strengths,for example, of less than approximately 8,000 V/cm, multiple ions mayhave the same mobility. However, as the electric field strengthsincrease, the different species diverge in their response such thattheir mobility varies as a function of the applied electric field. Thisshows that ion mobility is independent of applied RF field voltage atrelatively low RF field strengths, but is field-dependent at higher RFfield strengths.

FIGS. 2A and 2B demonstrate that species can have a unique behavior inhigh fields according to mobility characteristics. The ions passingthrough the filter are detected downstream. The detection signalintensity can be plotted as a characteristic detection peak for a givenRF field voltage and field compensation voltage Vcomp. Peak intensity,location, and shape are typically used for species identification.

However, a problem occurs in that the peaks, as seen in the typical DMSspectra, are generally broad in width. Therefore, compounds exhibitingintensity peaks at similar compensation voltages may be difficult toseparate from each another. Consequently, there may be particularconditions under which two different chemicals generateindistinguishable scans for a particular Vcomp and a particular RF fieldvoltage, or for other combinations of filter field/flow channelparameters. In such a case, it is may not be possible to differentiatebetween the two different compounds. Another problem may occur when twoor more chemical species have the same or almost the same ion mobilitycharacteristic for a particular set of field/flow channel parameters.This is most likely to happen in the low electric field regime (referredto herein as Ion Mobility Spectrometry or IMS), where many existing ionmobility spectrometer systems operate. Therefore, if two or morechemical species have the same or almost the same mobilitycharacteristic, then their spectroscopic peaks will overlap, andidentification and quantification of individual species will bedifficult or impossible.

FIG. 4 is a graph of Vcomp versus Vrf according to an illustrativeembodiment of the invention, but also highlighting the above describedprior art drawback. More particularly, FIG. 4 depicts a graph of Vcompversus Vrf for four compounds: lutidine; cyclohexane; benzene; anddimethyl-methyl-phosphonate (DMMP). Each curve shows the location ofdetected ion intensity peaks, such as those circled at 100, at thevarious (Vrf, Vcomp) locations, which in total provide the peakcharacteristics for each particular compound. As shown, there is aregion 100 in which the intensity peaks and mobility curves for DMMP andcyclohexane overlap with each other. As can be seen, operating in a Vrfregion of from approximately 2,500 Vpeak to approximately 2,650 Vpeak,at a Vcomp of about −6 Vdc to about −8 Vdc, one would find it virtuallyimpossible to discriminate between the two compounds based on a singleVcomp scan at a single Vrf. Specifically, in a conventional spectralscan approach that plots intensity/abundance versus Vcomp over a rangeof Vcomp for a single Vrf plots the overlapping peaks as a single peak.

Another drawback of conventional mobility based ion detection systems isthat they are susceptible to competitive ionization, such as atmosphericpressure competitive ionization (APCI). APCI occurs when one compound ispreferentially ionized over another compound. If a desired compound isnot ionized into an ion species, a mobility-based detector will notidentify or detect the presence of that compound. Systems have beendeveloped that remove compounds from a sample that preferentially ionizeto enable a desired compound to then be ionized and detected. Forexample, a gas chromatograph (GC) has been employed as a front end for aDMS to pre-separate a sample into its constituent compounds beforedetection. However, GCs are generally slow, and add complexity andexpense to mobility-based detection systems.

Also, conventional mobility based ion detection systems are notsensitive enough to detect very small amounts of chemical or biologicalagents which may pose a health risk to humans.

Accordingly, there is a need for improved ion mobility based compoundidentification using sample ion species pre-separation andamplification.

SUMMARY OF THE INVENTION

The invention addresses the deficiencies of the prior art by providing,in various embodiments, improved mobility based systems, devices andmethods for analyzing constituents in a sample. More particularly, invarious embodiments, the invention provides for improved sampledetection using techniques, such as ion species pre-separation and/orion species amplification.

As discussed above, atmospheric pressure competitive ionization (APCI)may cause compounds with the highest proton affinity (PA) and/or highestelectron affinity (EA) to capture preferentially or take up the chargefrom an ionization source. If there is a limited amount of chargeavailable, for example, in a compact DMS system with limited powerresources, the amount of available charge may not be sufficient tocharge or ionize all of the molecules in a sample matrix. Thus, if onlysome of the molecules in a sample matrix are ionized, only that limitedamount of molecules may be detected, resulting in erroneous analysis ofa chemical matrix. Furthermore, certain compounds may not be ionized dueto APCI, resulting in no detection of these compounds.

According to one aspect, the invention pre-separates certain ion speciesof a sample to reduce, and in some cases, eliminate the problem ofcompetitive ionization within ion based mobility detection analyzers.The invention includes embodiments that eliminate or mitigate theeffects of competitive ionization by separating ion species beforesample detection to prevent one ion species from consuming the chargeintended to be used to ionize another ion species.

According to one embodiment, neutrals, i.e., molecules of a sample thatare not ionized, are mixed with a new supply of charge, e.g., reactantions or a plasma field, to enable further APCI reactions to occur. Thenewly created ions may then be removed for analysis or simply discarded.This process may be repeated until a desired compound type is ionizedand detected using an analyzer.

In one implementation, a sample matrix is exposed to an ionizationsource to cause particular compounds in the sample to be ionized, theionized compounds to be removed, and the residual neutrals to bere-circulated. The ionization source may be, for example, an UV source,laser, plasma source, soft X-ray source, or reactant ions. Repeatedinterrogation of chemical compounds in a sample based on competitiveionization and the reaction of residual and/or un-reacted neutralsprovides a comprehensive measure of the chemical composition of thesample, without the need for traditional GC techniques.

The process of competitive ionization and the removal of product ionsmay be repeated, enabling incremental isolation of product ions andneutrals. Additionally, chemical ionization may be employed to injectfresh charge using reactant ions.

According to one aspect, the invention ionizes sample molecules to causea subset of the sample molecules to combine to form first product ions.It then separates the first product ions from a first un-ionized groupof sample molecules. Next, it ionizes a subset of the first un-ionizedgroup of sample molecules to form second product ions, and separates thesecond product ions from a second un-ionized group of sample molecules.

In one embodiment, the invention flows the first un-ionized group ofsample molecules and the first product ions through a first field toseparate the first product ions from the first un-ionized group ofsample molecules. According to one implementation of this embodiment,the inventions flows the second un-ionized group of sample molecules andthe second product ions through a second field to separate the secondproduct ions from the second un-ionized group of sample molecules. Insome implementations, the first and second fields are the same field.However, in other implementations, the first and second fields aredifferent fields.

In an alternative embodiment, the invention employs a mechanicalseparation for separating the first product ions from the firstun-ionized group of sample molecules. According to another alternativeembodiment, the invention employs a chemical process for separating thefirst product ions from the first un-ionized group of sample molecules.

According to another embodiment, the invention, subsequent to extractingthe second product ions, ionizes a subset of the second un-ionized groupof sample molecules to form third product ions, and separates the thirdproduct ions from a third un-ionized group of sample molecules.

The invention employs various approaches for ionizing the samplemolecules. In some instances, the invention mixes the first reactantions with the sample molecules to form the first product ions. Theinvention may also mix the second reactant ions with the firstun-ionized group of sample molecules to form the second product ions.According to one feature, the invention controls an effluent flow tocontrol contact time between the first reactant ions and the samplemolecules. According to another feature, the invention injects the firstreactant ions into a flow of the sample molecules to mix the samplemolecules to with first reactant ions.

According to one approach, the invention exposes the sample molecules toa first ionization source to form the first product ions, andre-circulates the first un-ionized group of sample molecules to exposethem to the first ion source to form the second product ions. Accordingto an alternative approach, the invention exposes the sample moleculesto a first ion source to form the first product ions, and flows thefirst un-ionized group of sample molecules to expose them to a secondion source to form the second product ions.

According to one embodiment, the invention flows the sample moleculesalong a first flow path past a first ionization source to form the firstproduct ions and then directs the first product ions along a second flowpath to separate the first product ions from the first un-ionized groupof sample molecules. The invention may further flow the first un-ionizedgroup of sample molecules past a second ionization source in the firstflow path to form the second product ions and then direct the secondproduct ions into the second flow channel to separate the second productions from a second un-ionized group of sample molecules. The inventionmay further flow the second un-ionized group of sample molecules past athird ionization source in the first flow channel to form the thirdproduct ions and then direct the third product ions into the second flowchannel to separate the third product ions from a third un-ionized groupof sample molecules.

The invention employs various approaches to directing product ions. Insome instances, the directing includes attracting the first product ionsinto the second flow channel. In other instances, the directing includesdeflecting the first product ions into the second flow channel. Thedirecting may also include directing the first product ions into thesecond flow channel via an opening in a barrier between the first andsecond flow channels. In certain instances, the first flow path includesa substantially cylindrical portion while the second flow channel issubstantially enclosed. Alternatively, the second flow path may besubstantially unenclosed.

In certain embodiments, the invention mixes the sample molecules withone or more dopants to improve separation of the first product ions fromthe first un-ionized group of sample molecules. The dopants may includeany one or combination of methylene bromide (CH₂Br₂), methylene chloride(CH₂Cl₂), chloroform (CHCl₃), water (H₂O), methanol (CH₃OH), andisopropanol.

According to another aspect, the invention ionizes sample molecules tocause a subset of the sample molecules to combine to form first productions and separates the first product ions from a first un-ionized groupof sample molecules. Subsequent to separating the first product ions,the invention ionizes a subset of the first un-ionized group of samplemolecules to form second product ions and separates the second productions from a second un-ionized group of sample molecules. Then, theinvention analyzes the sample based at least in part on the first andsecond product ions.

In one embodiment, the invention flows the first and second product ionsto the first analyzer and processes the information from the firstanalyzer about the first and second product ions to perform an analysisof the sample. In an alternative embodiment, the invention flows thefirst product ions to a first analyzer, flows the second product ions toa second analyzer, and processes the information from the first andsecond analyzers about the first and second product ions to perform ananalysis of the sample. The first and second analyzers may be in seriesor parallel with each other. In certain instances, the inventionanalyzes the sample based at least in part on at least one of the firstand second groups of un-ionized sample molecules.

In another embodiment, the invention directs the first product ions froma first flow channel into an analyzer flow channel and causes a flowfrom the analyzer flow channel toward a first flow channel containingthe first product ions and the first group of un-ionized samplemolecules. The flow is directed from the analyzer to inhibit the firstun-ionized groups of sample molecules from entering the analyzer flowchannel.

In another embodiment, a system for pre-separating a sample includes afirst ionizer for ionizing sample molecules to cause a subset of thesample molecules to combine to form first product ions and a firstseparator for separating the first product ions from a first un-ionizedgroup of sample molecules. The system also includes a second ionizer forionizing a subset of the first un-ionized group of sample molecules toform second product ions and a second separator for separating thesecond product ions from a second un-ionized group of sample molecules.The first and second ionizers may be the same ionizer or differentionizers. Also, the first and second separators may be the sameseparator or different separators.

In another embodiment, a compact DMS system includes a samplepre-separation unit for pre-separating product ions from un-ionizedsample molecules, a filter unit for passing particular ones of theproduct ions, and a detection unit for detecting the particular ones ofthe product ions passed by the filter unit.

In addition to being used for analysis, the invention may be used forselectively cleaning and/or conditioning samples, e.g., for removingselected molecules from a sample stream. For example, certainsemiconductor industry or other process control applications requireultra pure or clean gasses. In these processes, water molecules areconsidered a contaminant in a gas stream of Nitrogen or Argon. Incertain embodiments of the invention, water within a gas sample may bepreferentially ionized and then removed from the gas stream whilepurified Argon or Nitrogen are then used in a low pressure chemicalvapor deposition or for another semiconductor application.

While current mobility based analyzers such as DMS, IMS, and MS systemsare sensitive, there is a need to detect concentrations in ranges lowerthan parts-per-trillion (ppt). For instance, a very small number ofanthrax spores may cause significant health effects. However, existinganalyzers may not be sensitive enough to detect the charge generated bysuch a small number of spores. One technique for overcoming thislimitation involves concentrating and/or amplifying the number ofmolecules of a sample, in time, to enable an analyzer to produce alarger signal for detection.

In embodiment, the invention ionizes the molecules of a sample and thenfilters the ionized sample to pass particular ion species of a sampleconstituent to a detector. The invention mixes the constituent from thedetector with additional molecules of the sample and then ionizes themixture of the constituent and the additional molecules of the sample.The invention then filters the ionized mixture to pass a concentrationof the particular ion species of the constituent to the detector. Thepreceding steps of mixing, ionizing, and filtering may be repeated untila desired concentration of the particular ion species of the constituentis achieved and detected.

In other embodiments, the invention provides improved sample collection,filtration, detection, measurement, identification and/or analysis(collectively “analysis”) using, for example: dispersioncharacteristics; sample fragmentation; and/or sample processingvariations, such as and without limitation, variations in flowchannel/filter field conditions. Such conditions may include, anyspectral changes, including, without limitation changes in: pressure;temperature; humidity; field strength, duty cycle, and/or frequency;field voltage amplitude, frequency and/or duty cycle; detector biasvoltage magnitude and/or polarity; and/or filter field compensationvoltage magnitude and/or polarity.

In one practice, the invention employs one or more of the above toprovide a library of spectral signatures for a plurality of knownspecies, and identifies unknown species by comparing at least a portionof a spectral signature for the unknown species to at least a portion ofone or more of the spectral signatures stored in the library. Thespectral signature is a compilation of spectral information for aparticular species. The spectral information may include, withoutlimitation, spectral peak amplitude; spectral peak width; spectral peakslope; spectral peak spacing; spectral peak quantity; relative shifts inspectral peaks due, for example, to changes in processing conditions;spectral discontinuities; Vrf versus Vcomp characteristics or any othercharacteristics of any of the above described conditions plotted againstany one or more other above described conditions.

According to one aspect, the invention provides improved ion-basedsystems, methods and devices for analyzing samples by varying a firstsample processing condition over a first plurality of values, and one ormore second sample processing conditions over a second plurality ofvalues to determine spectral information for a sample. In one particularembodiment, the invention scans a field compensation voltage Vcomp overa range of values for one or more Vrf values to generate a spectralrepresentation at each of the one or more Vrf values.

According to one feature, the invention adjusts a third sampleprocessing condition to narrow the widths of the resulting spectralpeaks of the determined ion spectral information. Such width reductionreduces spectral peak overlap for samples having similar mobilitycharacteristics, improves resolution of an ion mobility-based analyzer,and thus, provides more accurate discrimination between sample species.In one configuration, the third sample processing condition includespressure in a sample flow channel, and the invention reduces thepressure in the sample flow channel to decrease the width of thespectral peaks.

According to another feature, the invention adjusts a third sampleprocessing condition to change a location of the resulting spectralpeaks of the determined ion spectral information, relative to a Vcomp atwhich they occur. Since peaks of differing species may shiftdifferently, such shifts can provide improved discrimination betweenpeaks of species having similar mobility characteristics. In oneconfiguration, the third sample processing condition includes Vrf, andthe invention applies more than two field voltages Vrf to provide peakshifting information for species identification.

According to another feature, the invention adjusts a third sampleprocessing condition to provide spectral information regarding bothpositive and negative ions of the sample. More particularly, in oneconfiguration, the invention provides both negative and a positive biasvoltages to multiple detector electrodes concurrently or to a singledetector electrode alternatively to provide both negative and positivemode scans. Since compounds that have similar ion mobilitycharacteristics relative to one mode may have differing ion mobilitycharacteristics relative to the other mode, adjusting the polarity of abias voltage to detector electrodes can further improve sample analysis.

In a further embodiment, the invention employs various n-dimensionalrepresentations of ion spectral information, to enhance the quality ofspectral signatures, improve differentiation between species havingsimilar ion mobility characteristics, and thus, improve identificationaccuracy, specifically, and sample analysis, generally. By way ofexample, in one configuration, the invention scans Vcomp for >2 fieldvoltages Vrf, to capture additionally, for example, spectral peak shiftinformation. The invention then generates an n-dimensionalrepresentation of the spectral information that aggregates the spectralinformation captured by scanning Vcomp at each Vrf. In one example, then-dimensional representation is a two-dimensional plot of Vrf versusVcomp aggregating the spectral information captured by scanning Vcomp ateach of the >Vrf field voltages. In a further example, the aggregatedrepresentation is a three-dimensional representation aggregating thespectral information captured from scanning Vcomp at the >2 Vrf fieldvoltages.

According to one approach, the three-dimensional representation is aplot of ion intensity as a function of Vrf and Vcomp. According to oneimplementation, Vcomp and Vrf are represented in special coordinates,such as x- and y-coordinates, and variations in ion intensity at the(Vcomp,Vrf) coordinates is represented in variations of anycolor-related feature, including without limitation, variations in grayscale, color saturation, or color at those coordinates. Suchcolor-related representations provide easily recognized distinctionsbetween species that were difficult or impossible to distinguishbetween, without the n-dimensional aggregation of the invention.

In a related implementation, a curve circumscribing the color-relateddifferences may be generated and the color-related differencesthemselves may be discarded. In this way, the invention can provide atwo-dimensional representation of the spectral peaks, for example, on aVcomp versus Vrf grid, while still incorporating the spectralinformation captured by scanning Vcomp over a plurality of Vrf values.In another alternative implementation, Vcomp, Vrf, and ion intensity aremapped into a three-dimensional (x,y,z) spatial representation.

According to a related embodiment, any or all of the spectralinformation may be represented in n-dimensional space as a function ofany or all of the processing variations to create >3 dimensionalspectral signatures for both known and unknown species. Conventionaln-dimensional cluster matching techniques may then be employed foridentifying the unknown species.

In any of the above described n-dimensional representations, any or allof the spectral information represented may be incorporated into thespectral signatures for known species and stored in the library of suchsignatures. Conventional pattern recognition techniques may be employedto correspond at least portions of the spectral signatures from unknownspecies with at least portions of the signatures from known samplesstored in the library to identify the unknown species. In otherimplementations, both the library of signatures and the capturedsignatures from the unknown species are represented as mathematicaldescriptions, and any suitable approach for making comparisons betweensuch mathematical descriptions may be employed to identify the unknownspecies.

According to another embodiment, the invention employs fragmentation toimprove DMS analysis. Fragmentation includes breaking large molecules ofsamples into smaller molecules, molecule clusters, components, and/orbase elements. The fragments may then be individually analyzed, inseries and/or in parallel to generate more spectral information for thesample than would be otherwise available without fragmentation.Fragmentation may be achieved, for example and without limitation, byusing any one or a combination of a chemical reaction, a high energyfield strength, high Vrf, heating, laser light, colliding the samplemolecules with other molecules, soft x-ray, electromagnetic waves, orthe like. According to one feature, the invention incorporates any orall of the above described spectral information for the fragmentspectral peaks into the spectral signature. According to a furtherfeature, the invention incorporates the point (e.g. the temperature,pressure, field strength, Vrf, colliding molecule mass, collidingmolecule velocity, laser intensity, laser frequency, x-ray intensityetc.) into the spectral signature.

According to other aspects, the invention provides various serial andparallel combinations of ion-based analyzers employing features,including those summarized above. In additional aspects, the inventionprovides various compact, handheld, lightweight and low power basedanalyzers, for example, for detecting chemical warfare agents (CWAs),Toxic Industrial Compounds (TICs), and/or Toxic Industrial Materials(TIMs).

The invention will now be described with reference to variousillustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

The foregoing and other objects, features, advantages, and illustrativeembodiments of the invention will now be described with references tothe following drawings in which like reference designations refer to thesame parts throughout the different views. These drawings are notnecessarily drawn to scale, emphasis instead being placed uponillustrating principles of the invention.

FIG. 1 is a graph depicting an asymmetric field having a peak RF, timeperiod, and duty cycle.

FIGS. 2A and 2B are graphs showing ion abundance (intensity) versusapplied field compensation voltage for acetone alone and for acombination of ortho-xylene and acetone, respectively, as detected in afield asymmetric ion mobility spectrometer.

FIG. 3 is a graph of ion mobility versus electric field strength forthree different compounds in a differential mobility spectrometer (DMS).

FIG. 4 is a graph of Vrf versus Vcomp indicating intensity peaklocations according to an illustrative embodiment of the invention andconceptualizing drawbacks of prior art approaches.

FIG. 5 is a conceptual diagram of a DMS according to an illustrativeembodiment of the invention.

FIG. 6 is a graph of ion intensity versus field compensation voltage forpositive mode spectra for a sample containing various amounts of ethylmercaptan as measured in a DMS.

FIG. 7 is a graph of ion intensity versus compensation voltage fornegative mode spectra of a sample containing various amounts of ethylmercaptan.

FIG. 8 is a graph of ion intensity versus field compensation voltageillustrating negative mode separation between monomer and reactant ionpeak (RIP) detections for sulfur hexafluoride (SF6).

FIG. 9 is a graph of ion intensity versus field compensation voltageillustrating the positive mode separation between monomer and reactantion peak (RIP) detections for sulfur hexafluoride (SF6).

FIG. 10 is a graph of ion intensity versus field compensation voltageillustrating a DMS response at various RF voltage levels in the negativeion mode and also showing the RIP detected in absence of SF6.

FIG. 11 is a graph of ion intensity versus field compensation voltageillustrating a DMS response in the positive ion mode where the SF6 peakis not isolated from the RIP.

FIG. 12 is graph of ion intensity (abundance) versus field compensationvoltage illustrating an ability to improve discrimination betweendetected ion species by observing ion spectral peak shifts correspondingto a change in field strength.

FIGS. 13A and 13B are graphs of ion intensity (abundance) versus fieldcompensation voltage illustrating an ability to improve discriminationbetween detected ion species by observing ion spectral peak shifts dueto reducing field strength.

FIGS. 14A and 14B are graphs of ion intensity at multiple fieldstrengths versus field compensation voltage, showing the affect ofchanges in compensation voltage on specific spectra, and show thedivergent behavior of monomer, cluster, and reactant ion peak (RIP)detections with changes in field strength and field compensationvoltage.

FIG. 15A is a three-dimensional color dispersion plot illustratingdetection of methyl salicylate over a range of field voltages and fieldcompensation voltages with varying ion intensity represented in varyingcolor according to an illustrative embodiment of the invention.

FIG. 15B is a two-dimensional graph of ion intensity versus fieldcompensation voltage for methyl salicylate at a single field voltage.

FIG. 16A is a three-dimensional color dispersion plot illustratingdetection of DMMP over a range of field voltages and field compensationvoltages with varying ion intensity represented in varying coloraccording to an illustrative embodiment of the invention.

FIG. 16B is a two-dimensional graph of ion intensity versus fieldcompensation voltage for DMMP at a single field voltage.

FIG. 17 is a three-dimensional color dispersion plot illustratingdetection of DIMP over a range of field voltages and field compensationvoltage with varying ion intensity represented in varying coloraccording to an illustrative embodiment of the invention.

FIG. 18 is a two-dimensional graph of ion intensity versus fieldcompensation voltage for DIMP at a single field voltage.

FIG. 19 is a graph of ion intensity at a plurality of field voltagesversus field compensation voltage illustrating the effects of changes infield conditions on location of individual detection peaks and theability to separate the detection.

FIG. 20A is a graph of ion intensity versus field compensation voltageillustrating the separation of detection peaks at different compensationvoltages between light and heavy molecules according to an illustrativeembodiment of the invention.

FIG. 20B is a graph of ion intensity versus field compensation voltageshowing the increase in number of peaks detected after samplefragmentation according to an illustrative embodiment of the invention.

FIG. 21 is a conceptual diagram of a DMS system using fragmentationoperating in parallel with a DMS system not using fragmentation toimprove sample analysis according to an illustrative embodiment of theinvention.

FIG. 22 is a conceptual diagram of a DMS system not using fragmentationoperating in series with a DMS system using fragmentation to improvesample analysis according to an illustrative embodiment of theinvention.

FIG. 23A is a graph of ion intensity versus field compensation voltageshowing peak detection for the DMS system of FIG. 22 not usingfragmentation.

FIG. 23B is a graph of ion intensity versus field compensation voltageshowing peak detection for the DMS system of FIG. 22 usingfragmentation.

FIG. 24 is a conceptual block diagram of a DMS system including afragmentation region according to an illustrative embodiment of theinvention.

FIG. 25 is a three-dimensional color dispersion plot illustratingdetection of agent GA according to an illustrative embodiment of theinvention.

FIGS. 26A-26H are two-dimensional graphs of ion intensity versus fieldcompensation voltage at particular field voltages, the two-dimensionalgraphs being of the type combinable into the three-dimensional colordispersion plot of FIG. 25, according to an illustrative embodiment ofthe invention.

FIGS. 27A and 27B are graphs of ion intensity at a plurality ofpressures versus field compensation voltage according to an illustrativeembodiment of the invention.

FIGS. 28A and 28B are graphs of ion intensity versus pressure showing aquantifiable effect on positive and negative background spectra,respectively, caused by a decrease in pressure according to anillustrative embodiment of the invention.

FIGS. 29A and 29B are graphs of ion intensity at a plurality ofpressures versus field compensation voltage showing the effect ofvarying pressure on negative and positive tert-butylmercaptan ortert-butylithiol (TBM) spectra, respectively, according to anillustrative embodiment of the invention.

FIGS. 30A and 30B are graphs of ion intensity versus pressure showingthe effect of varying pressure on negative and positive TBM ion peakparameters, respectively, according to an illustrative embodiment of theinvention.

FIG. 31 is a graph that shows the effect of reduced pressure on analytepeaks for chemical warfare agents such as DMMP, DIMP, and MS.

FIGS. 32A-32D are graphs of ion intensity versus field compensationvoltage showing improved detection resolution for agent GF at reducedpressures according to an illustrative embodiment of the invention.

FIG. 33 is a three-dimensional color dispersion plot illustratingdetection of positive ions of 0.005 mg/m³ DIMP at about 0.65 atm andover a range of field voltages and field compensation voltages withvarying intensity depicted by varying colors.

FIG. 34 is a three-dimensional color dispersion plot illustratingdetection of positive ions of 0.005 mg/m³ DIMP at about 0.5 atm and overa range of field voltages and field compensation voltages with varyingintensity depicted by varying colors.

FIG. 35 is a graph that shows positive (left) and negative (right)three-dimensional color dispersion plots for 0.85 mg/m³ agent GB with arelative humidity (RH)=87 in a DMS system operating at 0.5 atm and for afragmented sample.

FIGS. 36A and 36B are graphs that show a plot of compensation versusfield strength of detected monomer and cluster ion peaks for a family ofketones according to an illustrative embodiment.

FIGS. 37 and 38 are tables, each including a collection of detectiondata for a group of monomer and dimers (clusters) of eight ketonesrespectively, that were used to generate the curves in the graphs ofFIGS. 36A and 36B.

FIGS. 39A and 39B are graphs of a ratio of field strength to gas density(E/N) versus field compensation voltage that illustrate the results ofcalculating normalized alpha parameter curves.

FIG. 40A is a flow diagram of an exemplary sequence of steps of acomputer process used to acquire data concerning a particular chemicalion species.

FIG. 40B shows a diagram of a data structure for a library of storedcompound data measurement information.

FIG. 40C is a flow diagram of a series of steps that may be applied toperform a chemical recognition.

FIG. 40D is a flow diagram of a series of steps that may be added to thedata acquisition and chemical recognition processes using alpha curvefitting.

FIG. 40E shows a diagram of a more complex data structure.

FIG. 40F is a flow diagram of a sequence of processes that may be usedto distinguish monomer and cluster peak responses.

FIG. 40G is a flow diagram of a process showing the combination ofmonomer and cluster scoring.

FIG. 41 is a conceptual diagram of a compact DMS analyzer system 1400used to detect and identify chemical warfare agents (CWAs), ToxicIndustrial Compounds (TICs) and Toxic Industrial Materials (TIMs) whichmay be released in warfare or terrorist situations according to anillustrative embodiment of the invention.

FIG. 42 is a graph of multiple plots showing experimental results for aseries of warfare agent simulants selectively mixed with 1% headspace ofAFFF.

FIG. 43 is a three-dimensional color dispersion plot of the detection ofpositive ions of agent GA over a range of field voltages and fieldcompensation voltages with varying intensity represented in varyingcolor according to an illustrative embodiment of the invention.

FIG. 44 is a conceptual block diagram of a chemical and/or biologicalagent detection system using an ion mobility analyzer system, membrane,and recirculation system according to an illustrative embodiment of theinvention.

FIG. 45 is a conceptual block diagram of a chemical and/or biologicalagent detection system configured for reduced pressure analysisaccording to an illustrative embodiment of the invention.

FIG. 46 is a conceptual block diagram of a chemical and/or biologicalagent detection system using a cylindrical DMS analyzer system,recirculation system, and multiple flow channels according to anillustrative embodiment of the invention.

FIGS. 47-53 are conceptual block diagrams respectively of chemicaland/or biological agent detection systems using various configurationsof a DMS analyzer system, recirculation system, and other componentsaccording to an illustrative embodiment of the invention.

FIG. 54A is a conceptual diagram showing a pre-separation process of asample matrix according to an illustrative embodiment of the invention.

FIG. 54B is a conceptual diagram showing a pre-separation process of asample matrix according to another illustrative embodiment of theinvention.

FIG. 55 is a conceptual block diagram of a sample pre-separation systemusing a first and second ionization region and first and seconddeflector regions to separate a sample matrix according to anillustrative embodiment of the invention.

FIG. 56A is a conceptual diagram of a sample pre-separation processwhere a sample matrix may be re-circulated multiple times to interactwith an ionization source such as reactant ions to sequentially removediffering compound product ions according to an illustrative embodimentof the invention.

FIG. 56B is a conceptual diagram of a sample pre-separation processwhere a sample may be re-circulated multiple times to interact with anionization source, such as an electric or magnetic field, tosequentially remove differing compound ions according to an illustrativeembodiment of the invention.

FIG. 57 is a conceptual block diagram of a sample pre-separation systemcapable of re-circulating a sample through an ionization region multipletimes to sequentially remove differing compound ions having differingproton or electron affinities according to an illustrative embodiment ofthe invention.

FIG. 58A is a conceptual diagram of a sample pre-separation system whereselected ions are intermixed with a sample to enable the pre-separationof ions having a particular proton or electronic affinity according toan illustrative embodiment of the invention.

FIG. 58B is a conceptual diagram of a sample pre-separation system whereselected ions, having been filtered and pre-selected, are thenintermixed with a sample to enable the pre-separation of ions having aparticular proton or electronic affinity according to an illustrativeembodiment of the invention.

FIG. 59A is a conceptual diagram of a sample pre-separation systemincluding two flow channels and multiple (and optionally different)ionization sources for selective ion separation from a sample matrixaccording to an illustrative embodiment of the invention.

FIG. 59B is a conceptual diagram of a sample pre-separation systemhaving two flow channels and multiple (and optionally different)ionization sources for selective ion separation from a sample matrixwhere at least one of the ionization sources is a plasma ionizationsource.

FIG. 60 is a graph of ionization energies required for various NOx ionspecies to form either positive or negative ions by direct photoionization in air.

FIG. 61A is a graph of relative intensity versus mass units showing themass-spectra to positive NOx ion NO.

FIG. 61B is a graph of relative ion intensity versus mass units showingthe mass-spectra for positive NOx ion NO₂.

FIG. 61C is a graph of ion intensity versus field compensation voltageshowing the ion intensity peaks for NO and NO₂.

FIG. 62 is a conceptual diagram of a cylindrical sample pre-separationsystem including an integrated cylindrical DMS or other analyzeraccording to an illustrative embodiment of the invention.

FIG. 63 is a conceptual block diagram of a sample pre-separation systemcapable of mixing dopants with a sample matrix in a controlled mannerbefore or after the reactant ions are added according to an illustrativeembodiment of the invention.

FIG. 64 is a conceptual diagram of an array of logic circuits includingan “or” flow circuit and an “and” flow circuit used to cause multipleand different ions to interact and form a desired reactant ion speciesaccording to an illustrative embodiment of the invention.

FIG. 65 is a conceptual diagram of a sample pre-separation and analysissystem using multiple ionization zones and multiple analyzers to analyzevarious ions of a sample matrix according to an illustrative embodimentof the invention.

FIG. 66 is a conceptual diagram of a sample pre-separation and analysissystem using multiple ionization zones and DMS analyzers, including aDMS with a drift tube and ion filter region arbitrarily curved,according to an illustrative embodiment of the invention.

FIG. 67 is a conceptual diagram of a sample pre-separation and analysissystem employing multiple ionization zones and analyzers along with afiltered gas source to control pressure within the analyzers accordingto an illustrative embodiment of the invention.

FIG. 68 is a flow diagram of a sample analysis process including samplere-circulation and pre-separation according to an illustrativeembodiment of the invention.

FIG. 69 is a flow diagram of a process showing the analysis of a samplematrix composed of multiple molecule species according to anillustrative embodiment of the invention.

FIG. 70 is a conceptual diagram of a sample pre-separation (neutralsremoval) system where the neutral molecules are removed from the ionizedmolecules rather than removing the ions from the neutral gas stream.

FIG. 71 is a conceptual diagram of a sample pre-separation systememploying an ionization region, DMS filter, deflector, pump, and valveto selectively filter an ion species for analysis according to anillustrative embodiment of the invention.

FIG. 72 is a conceptual diagram of a sample pre-separation systememploying an ionization region, ion guiding region, DMS ion filter,positive and negative ion deflectors, optional analyzers, flowgenerator, selective concentrator and valve for ion species analysisaccording to an illustrative embodiment of the invention.

FIG. 73A is a conceptual diagram of a sample amplification systememploying a DMS filter, detector and neutralizer, and recirculation loopfor selected ion species analysis according to an illustrativeembodiment of the invention.

FIG. 73B is a conceptual diagram of a sample amplification systememploying a DMS filter, detector, ionization source, deflector, and anoptional DMS with a re-circulation channel for selected ion speciesanalysis according to an illustrative embodiment of the invention.

FIG. 74 is a conceptual diagram of a sample amplification and analysissystem employing a re-circulation channel according to an illustrativeembodiment of the invention.

FIG. 75 is a flow diagram of a process for amplifying a selected ionspecies using an analyzer, such as a DMS analyzer, according to anillustrative embodiment of the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

As described above in summary, the invention is generally directed tosystems, methods and devices for providing improved detection,measurement, discrimination and analysis (collectively “analysis”) ofcompounds. The compounds analyzed may include any compound, both organicand inorganic, without limitation elements, chemicals, and biologicals.In particular illustrative embodiments, the invention is directed toimproved ion mobility-based compound analysis. Particular features ofthe invention include, use of dispersion plots, sample fragmentationand/or pressure controls to improve discrimination between compoundshaving similar or overlapping ion mobility characteristics.

Although the illustrative embodiments of the invention are described interms of Field Asymmetric Ion Mobility Spectrometers (FAIMS), also knownas Differential Mobility Spectrometers (DMS), or Radio Frequency IonMobility Spectrometers (RFIMS) among other names (collectively DMS), thefeatures of the invention may be similarly employed in combination withion mobility spectrometry (IMS), time of flight (TOF) IMS, gaschromatography (GC), Fourier transform infrared (FTIR) spectroscopy,mass spectrometry (MS), and liquid chromatography mass spectrometry(LCMS).

FIG. 5 is a block diagram of a DMS system 10 of the type that may employthe invention. The system 10 includes a flow section 15 and a processorsection 40. The flow section 15 includes a flow channel 11 extendingfrom a flow inlet 12 to a flow outlet 13. Opposing filter electrodes 20and 21 are located within the flow channel 11. Detector electrodes 26and 30 are also located within the flow channel 11. The processorsection 40 includes an RF voltage generator 42 for providing an RF fieldvoltage to the filter electrodes 20 and 21, and direct current (dc)voltage generator 44 for providing a dc compensation voltage Vcomp tothe filter electrodes 20 and 21. The processor section 40 also includesa processor 46 for controlling the voltage generators 42 and 44, and forprocessing inputs from the ion detectors 28 and 30 by way of theamplifiers 36 and 38 the A/D converter 48. The processor section 40 alsoprovides a display 49 for providing analysis information to a user. Onefeature of the system 10 is that it may be contained in a hand held unitweighing less than about one pound.

In operation, a sample S enters the flow channel 11 at the flow channelinlet 12. The sample S may, for example, be drawn in from theenvironment or received from a front end device, such as another DMS, anIMS, TOFIMS, GC, FTIR, MS, or LCMS. The sample S may be mixed with aneffluent, such as a gas, liquid or vapor. In the instant example, acarrier gas CG is employed to flow the sample S through the flow channel11. Upon entering the flow channel 11, the sample S flows into anionization region 14. The sample is ionized by an ionization source 16as it flows through the ionization region 14, creating a set of ionizedmolecules 17+, 17−, with some neutral molecules 17 n, of variouschemical species in the sample S. This may include, for example, monomerions and cluster ions. Such clusters may be created when a monomercombines with water molecules or other background molecules, and thecombination is ionized.

The carrier gas CG then carries the ionized sample S into the ion filterfield 18 located between the opposing filter electrodes 20 and 21 of theion filter 24. Filtering proceeds based on differences in mobility inthe filter field 18 of the various ions included in the sample S. Ionmobility is influenced, for example, by ion size, shape, mass andcharge. The field generator 42 applies an asymmetric field voltage Vrfacross the filter electrodes 20 and 21 to cause the field strengthwithin the filter field 18 to alternate between high and low fieldstrengths. The ions 17+, 17− and 17 n move in response to the field,based on their mobility characteristics. Typically, an ion's mobility inthe high field strength condition differs from its mobility in the lowfield strength condition. This mobility difference produces a nettransverse displacement of the ions as they travel longitudinallythrough the filter 24. The transverse displacement defines an iontrajectory for each of the sample S ions.

As described above, the voltage generator 44, under the control of theprocessor 46, applies a dc compensation voltage Vcomp across theelectrodes 20 and 21. The compensation voltage Vcomp causes particularion species to be returned toward the center of the flow path 14, andthus enables them to exit the filter field 18, without colliding witheither of the filter electrodes 20 or 21 and without being neutralized.Other species, for which the applied Vcomp is not sufficient ultimatelycollide with the filter electrodes 20 and 21 and are neutralized. Theneutralized ions are purged, for example, by the carrier gas CG, or byheating the flow path 11.

The illustrative system 10 of FIG. 5 also can discriminate between ionsbased on differences in polarity, as is the case with the ions 17− and17+. According to one feature, the system 10 of FIG. 5 can be operatedto concurrently, or in some instances, substantially simultaneouslydetect both positive and negative ions in the sample S. This featureenables identification of two compounds concurrently, or in someinstances, substantially simultaneously. This feature also enablesconcurrent or substantially simultaneous detection of two modes of asingle compound.

In operation, the two species of ions 17+ and 17−, enter the detectionregion 25, where further separation occurs followed by their intensitydetermination. In an illustrative embodiment, the electrode 28 of thedetector 26 may be positively biased to attract the ions 17− and repelthe ions 17+. Alternatively, the electrode 30 of the detector 26 may bebiased negatively to attract the ions 17+ while repelling the ions 17−.The signals generated by the ions collecting at the detector electrodes28 and 30 are amplified by respective amplifiers 36 and 38 and providedto the processor 46 by way of the A/D converter 48. According to onefeature, the processor 46 compares the digitized signals from the A/Dconverter 48, with a library of ion intensity curves for known compoundsstored in the memory 47, to identify compounds in the sample S. Theresults of the comparison operation can then be provided to anappropriate output device, such as the display 49, or may be provided toan external destination by way of an interface 56.

According to a further illustrative embodiment, the system 10 iscalibrated prior to employing it for analyzing a sample. Moreparticularly, the library of ion intensity curves for known species ofions at particular Vcomp and Vrf settings is created and stored in thememory 47. According to one feature, once the system 100 is calibrated,it may be used continuously, without need for further calibration.However, it is also within the scope of the invention to calibrate thesystem 10 using the reactant ion peak (RIP) or a dopant peak, forexample.

According to various illustrative embodiments, field strength within thefilter field 18 resulting from an applied field voltage Vrf may havevalues ranging from about 1,000 V/cm to about 30,000 V/cm, or higher.The frequency of Vrf may have values ranging from about 1 to about 20megahertz (MHz), with the higher frequencies having an approximately 30percent duty cycle.

It should be noted that the system 10 may be tuned by employing anysuitable operating values of, for example, Vrf, Vcomp, field strength,Vrf duty cycle, Vrf wavelength and Vrf frequency. Additionally, asdescribed in further detail below, to improve analysis, the system 10may be tuned by varying values of other flow channel conditions, such asand without limitation, temperature, pressure, humidity, flow rate,doping and carrier gas CG composition. As also described below in moredetail, multiple scans of the sample S taken, for example, byrecirculating the sample S and/or processing the sample in paralleland/or in series with one or more additional DMS, IMS, TOFIMS, GC, FTIR,MS, or LCMS, at differing flow channel and/or filter field conditionsmay be employed to improve analysis of the sample S.

According to one illustrative embodiment, the processor 46 causes thevoltage generator 44 to scan or sweep a range of field compensationvoltages Vcomp for a particular RF field strength as controlled by theapplied Vrf to obtain a first spectrum for the sample S. Then, Vrf isset to a different level and the Vcomp is once again scanned toestablish a second spectrum for the sample S. This information can becompared to a library of spectral scans in a similar fashion as thatdescribed above to identify a compound in a sample.

If a particular combination of peaks in a spectral scan is known toindicate the presence of a particular compound, data representing themultiple peaks can be stored and future detection data can be comparedagainst this stored data. For example, under controlled filter fieldconditions, such as at a raised field strength, a clustered compound maybecome de-clustered. The detection results in a signature of peaks thatcan be used to identify the source compound being detected even asdetected in a single scan.

According to one illustrative application, the invention is used fordetecting sulfur-containing compounds in a hydrocarbon background. Inone example, negative and positive ions are separately detected. Thedetected data enables a quantitative measurement of concentration ofthese sulfur-containing compounds, independent of the hydrocarbonbackground.

In another illustrative application, the invention is used for detectingtrace amounts (parts per million (ppm), parts per billion (ppb), orparts per trillion (ppt)) of mercaptan in varying and even highhydrocarbon backgrounds. The system 10 of FIG. 5 is also able tocharacterize hydrocarbon gas backgrounds. For example, the invention iscapable of detecting mercaptans, such as ethyl mercaptan in a methanebackground, and is also capable of detecting a gas, such as methane, ina mercaptan background.

In this practice of the invention, where mercaptans were detected inhydrocarbon background, the asymmetric voltage applied to the ion filterelectrodes ranged from about 900 to about 1.5 kV (high field condition),and a low voltage of about −400 to about −500 V (low field condition).The frequency ranged from about 1 to about 2 MHz, and the high frequencyhad an approximate 30% duty cycle, although other operating ranges maybe employed. In one embodiment, the detector electrodes were biased at+5v and −5 v. With this arrangement, the mercaptans can be detected bythe negative mode (−5v) detector and the hydrocarbon gases can bedetected by the positive mode (+5v) detector.

The system 10 employs various conventional components. By way ofexample, the amplifiers 36 and 38 may be Analog Devices model 459amplifiers. Additionally, the A/D converter may be included on aNational Instruments circuit component (model 6024E) for digitizing andstoring the scans, and may include software for displaying the resultsas spectra, topographic plots, dispersion plots or graphs of ionintensity versus time. Alternatively, such software may be stored in thememory 47 and may control the processor 46. The ionization source maybe, for example, a plasma, laser, radioactive, UV lamp, or any othersuitable ionization source.

According to one illustrative embodiment, Vrf is applied across thefilter electrodes 20 and 21. However in some configurations, Vrf isapplied to one filter electrode, e.g., electrode 20, and the otherelectrode, e.g., electrode 22, is tied to ground. Vcomp is then appliedto one of the filter electrodes 20 and 21, or alternatively, across thefilter electrodes 20 and 21, according to the ions species to be passed.According to another feature, the detector electrodes 28 and 30 arebiased with a floating bias, such as with the electrode 28 being biasedat −5 Vdc and the electrode 30 being biased at +5 Vdc, leads to goodperformance for detection of mercaptans in hydrocarbon or airbackgrounds.

FIG. 6 is a graph of ion intensity versus field compensation voltage for“positive mode” spectra for a sample containing varying amounts of ethylmercaptan as measured in a DMS system of the type depicted at 10 in FIG.5. For positive mode detection, the detector electrode 28 is negativelybiased and attracts positive methane ions 17 m+ for detection. FIG. 7 isa graph of ion intensity versus compensation voltage for “negative mode”spectra of a sample containing various amounts of ethyl mercaptan. Fornegative mode detection, the detector electrode 30 is positively biasedand attracts the negative mercaptan ions 17 m− for detection. As can byseen from FIGS. 6 and 7, the mercaptan signatures are capturedindependent of the air-hydrocarbon carrier gas CG background, at variousdosage levels and the detected sample peaks are fully isolated from thebackground. As can be seen in FIG. 6, the reactant ion peak (RIP) isisolated; and as shown in FIG. 7, the background (sample #9) is flat.

As mentioned above, the detector electrodes 28 and 30 can be oppositelybiased to enable concurrent, or in some configurations, substantiallysimultaneous detection of both positive and negative ions. Even in asample such as mercaptan, which when ionized may have predominantlynegative ions, detecting both positive and negative ions providesimproved analysis accuracy over a single mode detection approach. This,in turn, improves identification accuracy and confidence, and reducesthe likelihood of false positives and false negatives.

For example, Sulfur hexafluoride (SF6) can be well detected in thenegative mode. However, the response in the positive mode, while alonenot definitive, has a profile, and thus in combination with the negativemode, is confirmative and provides a lower likelihood of a falsedetection. According to one feature, the invention can detect SF6 insingle mode (e.g., only negative mode detection) or dual mode (bothnegative and positive mode detection), seriatim, concurrently, orsimultaneously.

SF6 gas is used in atmospheric tracer applications to monitor air flow,as a tracer for leak detection in pipes to point detect sources ofleaks, in power plants to isolate switches to reduce, or preventbreakdown of the switches, among other uses. Isolation and detection ofSF6 is often found to be a difficult proposition.

According to one illustrative application, a system of the invention isemployed to detect SF6 in air. According to a further illustrativeembodiment, the invention provides a portable, battery powered unit forthe detection of SF6 with a sensitivity of about 1×10⁻⁹ atm cc/sec SF6(0.01 PPM). In this illustrative embodiment, the invention may be used,for example, in the power industry to ensure the leak tightness of HighVoltage Switchgear and in the laboratory for testing fume hoods to theASHREA 110 specification. Other applications include torpedo head,pipework systems, and air bag integrity testing. The high sensitivity,rugged design and ease of use and set up of the invention areadvantageous for many applications that involve the detection of SF6.

FIG. 8 is a graph of ion intensity (y-axis) versus Vcomp (x-axis) fornegative mode detection of SF6 according to an illustrative embodimentof the invention. As can be seen, application of the invention providesa distinct peak for the SF6, separate from the reactant ion peak. FIG. 9provides a similar plot for SF6 for positive mode detection. As can beseen, for positive mode detection, there is no significant differencebetween the signal 51 without the SF6 present and the signal 53 with theSF6 present. FIG. 10 shows a plot of intensity (y-axis) versus Vcomp(x-axis) for SF6 at three different field voltages Vrf (shown at 57, 58and 61 for negative mode detection along with the RIP 55 detected inabsence of SF6. FIG. 11 shows a similar plot to that of FIG. 10, forpositive mode detection. As would be expected, the positive modedetection curves 69, 71 and 73, substantially track their correspondingRIP curves 63, 65 and 67, respectively. As mentioned above with respectFIG. 16, while alone this is not definitive, it is an expected detectionand therefore may be used as confirmative when combined with adefinitive SF6 negative mode detection.

According to another feature, the above described library data for knownion species intensity signatures for known device characteristics may beaccessed for either single mode or simultaneous positive and negativemode detections. By comparison with historical detection data for thedevice, these peaks can be more clearly identified as the tell-talespectra of the mercaptan. Both spectra give an indication of themercaptan, qualitatively and quantitatively. Although the advantages ofthe simultaneous positive and negative mode detection is described abovewith respect to mercaptan, they may be employed to the analysis of anysample, and are especially useful with real-time analysis of complexsamples, such as ones containing mercaptans and hydrocarbon gas, whichhave similar ion mobility characteristics, and are therefore, difficultto discriminate between.

The foregoing demonstrates favorably obtaining multiple detection datafrom a single mobility scan for identification of detected ion speciesin a sample. This innovation is useful in many applications.Notwithstanding this valuable innovation, a still higher level ofconfidence and further reduced false positives may be obtained by (1)obtaining multiple detection data from multiple ion mobility scans, and(2) further processing such data to extract device independentattributes, such as a mobility coefficient, α.

According to one illustrative “multiple scan” embodiment, ions areidentified based not on a single set of field conditions, but instead onmultiple ion intensity scans taken at least two and possibly additionalnumbers of field conditions (e.g., at least two field measurementpoints). Detections are correlated with the Vrf and Vcomp, at the atleast two different field conditions, to characterize a given detectedcompound. Because multiple detection data are associated with a givenion species of interest, more accurate detections can be made.Comparison with stored data results in reliable identification ofdetected compounds.

Strategies for identifying detected ions based on data in spectral peaksor in mobility curves include: curve matching, peak fitting,deconvolution (for overlapping peaks), multi-dimensional mapping, forexample, employing three-dimensional representations, including (x,y,z,etc.) spatial coordinate systems and/or (x,y, etc.) coordinate systems,with z- or other values represented by color variations. Thesetechniques enable identification of detected ion species based peaks ina single scan, including simultaneous positive and negative modedetections, and also in multiple scans. The goal is the same: analysisof multiple detection data that can be used to definitively identify,detect, measure or otherwise analyze the species of a detected ion.

As described above, different ion species of chemicals exhibit differentmobility as a function of the compensated applied Vrf. Thus, by applyinga set of different Vrf voltages and measuring the Vcomp at the ionabundance peak locations, for example, as detected by the detector 26 ofFIG. 1, for the various compounds, a family of measurement pointscharacteristic of a compound can be developed. This family of points canthen be plotted to determine the ion mobility curve signature forspecific species as a function of Vrf and Vcomp, for example, as shownin FIG. 4. As also described above, such data can be stored and comparedwith data from scans of unknown compounds to identify the unknowncompounds. While some comparison approaches perform curve matching,other approaches determine an ion intensity for a particular ion speciesfor two nearby field strength and Vcomp conditions. The slope betweenthe two data points is calculated and employed as a signature for theparticular ion species. The selection of measurement points and thenumber of measurement points may be adjusted for the specificityrequired for a particular application. The minimum number of measurementpoints is two, which at least identifies an aspect (such as slope) ofthe characteristic curve for a compound, given the known field values.

Although performing slope and/or curve matching for an individual or formultiple scans, where a single filter field/flow channel condition isvaried, may provide sufficiently accurate results for some applications,one illustrative embodiment of the invention recognizes that multiplescans taken while varying multiple filter field and/or flow channelconditions can provide improved results. By way of example, according toone illustrative embodiment, the invention steps Vrf through a pluralityof values and scans Vcomp at each of the plurality of Vrf values togenerate unique sets of data, which better distinguish between compoundsand, thus, provide more accurate identification of detected compounds.This approach can be employed to create a data store of more accurateion mobility signatures for compounds of interest.

According to one illustrative embodiment, the invention incorporatesinformation regarding shifts in an ion abundance peak for a particularion species at multiple filter field/flow channel conditions into thespectral signature for a compound. More specifically, at a particularVrf (Vrf1) an ion abundance peak may be detected at a particular Vcomp(Vcomp1). However, the ion abundance peak may shift to be detected at asecond Vcomp (Vcomp2) for a second Vrf (Vrf2). One illustrativeembodiment of the invention recognizes that, in many instances, the ionpeak shift from Vcomp1 to Vcomp2 in response to varying Vrf from Vrf1 toVrf2 is indicative of a particular ion species. Similar measurements ofunknown compounds can be compared against this portion of the spectralsignature to aid in identification of the unknown compound.

FIG. 12 depicts an example illustrating the above described ionabundance spectral shift due to a change in Vrf from 1400 Vpeak to 1450Vpeak over a scanned Vcomp. In FIG. 12, the peaks 110-1, 110-2, 110-3,and 110-4 occur at a particular field compensation voltages Vcomp, forVrf at 1400 Vpeak (corresponding to a field strength of 28,000 V/cm),but shift to be located at different compensation voltages in responseto Vrf being changed to 1450 Vpeak (corresponding to a field strength of29,000 V/cm). As can be seen from FIG. 12, even small changes in a fieldcondition, such as a change in Vrf, can cause a measurable ion peakshift, and can thus provide significant additional information to theion spectral signature. In the specific example of FIG. 12, the shift inion peak due to the change in Vrf is employed when making a comparisonto ion spectral signatures for known compounds to identify an unknowncompound.

FIGS. 13A and 13B show an experimental example illustrating how ionspectral peak shifting can be employed to identify an unknown species.In FIGS. 13A and 13B, in a field strength of about 24000 V/cm, peaks forthree different isomers of xylene in a sample, p-, o-, and m-, weredetected. In FIG. 13A, the peaks for p- and o- are indistinguishable,while the peak for m- is well defined. To further evaluate the sample, asecond detection (FIG. 13B) was performed at a lower field strength of18000 V/cm. As can be seen in FIG. 13B, the peak shift due to the changein field strength causes the three different isomers p-, o-, and m- ofxylene to be more clearly distinguishable, and thus more accuratelyidentified. As can be seen from FIGS. 13A and 13B, better discriminationbetween species is not always a result of applying a higher fieldstrength. More particularly, in this example, the p- and o-xyleneisomers become more distinguishable at a reduced field strength.

According to another illustrative embodiment and as mentioned above, theinvention generates detection data over a range of applied filterfield/flow channel conditions. For example, FIGS. 14A and 14B show theeffect of changes in field strength on the location of detection peaksat different Vcomp levels for hexanone and octanone, as detected in aDMS system of the type depicted at 10 in FIG. 1. The curves are offseton the vertical axis, with the offset increasing as electric fieldstrength increases. While various operating ranges are possible, as anillustration, FIGS. 14A and 14B may be understood as presenting peak Vrfbetween a low of about 620 Vpeak (lowermost plot in each) and a high ofaround 1450 Vpeak (uppermost plot in each). Several attributes are notedin this series of responses. For example, referring specifically to thehexanone plot of FIG. 14A, a monomer peak of 601-1 of particularinterest is somewhat obscured in the lowest field strength condition.However, at the highest applied field strength, the peak 601-mcorresponding to hexanone is clearly discernable from the other peaks.

Several phenomena have occurred with the increase in increasing appliedfield strength. First, a reactant ion peak (RIP) 605-1 is relativelydominant in the low field strength detection. However, as electric fieldstrength is increased, the RIP 605-m shifts to the left at a more rapidrate than the monomer ion peak 601-m of interest. This is because the αparameter for the mobility coefficient for the reactant ion species isdifferent than the α parameter for the monomer ion of interest.

In addition, the relative amplitude of the RIP 605 decreases markedlywith the increase in the electric field strength. Thus, RIP 605-m isobserved at much lower amplitude and well separated from the monomerpeak 601-m of interest at a specific field condition. While the monomerpeaks 601 also shift, they do not shift by the same amount, or by asmuch. Thus, by analyzing the compound over a range of applied fieldconditions, a condition can be discovered at which the RIP 605 shiftsaway from or off the scale of other observed peak voltages. In somecases, this allows easier detection of the monomer ion peak 601 ofinterest.

Similar behavior is observed in the monomer peaks 610-1, 610- . . . ,610-n observed for octanone and the resulting reactant ion peaks 615-1to 615-m. This information can thus be used to identify a species bycomparing a family of response curves to a stored family of knownresponse curves.

Another observed effect shown in both FIGS. 14A and 14B is that a groupof cluster ions 608 and 610 are seen. The cluster ions 608 representclusters of chemical materials in the sample. Typical cluster ions,having a heavier chemical weight, have peaks that are shifteddifferently from monomer ion peaks of interest. In this example, thecluster peaks shift in a direction away from the direction of shift ofthe monomer peaks with increasing applied field strength. Thischaracteristic feature of cluster ions, observed with this sample, canalso be stored and utilized in recognizing the hexanone and/or octononeions. The curves shown in FIGS. 14A and 14B are but one example of howapplying a range of field/flow channel conditions to detect a givensample can be utilized to an advantage.

As mentioned above briefly, according to one illustrative embodiment,the invention employs multi-dimensional compound signatures forcomparison with multi-dimensional representations of unknown compoundsto identify and more generally analyze the unknown compounds. Suchmulti-dimensional representations may arise, for example, from plottingion abundancy as a function of a plurality of varying filter field/flowchannel conditions. Such conditions may include, without limitation,Vrf, Vcomp, filter field strength, Vrf duty cycle, Vrf wavelength andVrf frequency; temperature, pressure, humidity, flow rate, doping andcarrier gas CG composition. Multi-dimensional representations may alsoresult from taking multiple scans of the sample S taken, for example, byrecirculating the sample S and/or processing the sample S in paralleland/or in series with one or more additional DMS, IMS, TOFIMS, GC, FTIR,MS, or LCMS, at the same or differing flow channel/filter fieldconditions. The multi-dimensional representation, according to oneillustrative embodiment, is a three-dimensional dispersion plot,employing x- and y-spatial coordinates, with a z-coordinate beingrepresented by a variation in color.

FIG. 15A shows a three-dimensional color dispersion plot 620 depictingdetection of methyl salicylate over a range of field voltages Vrf(y-axis) and field compensation voltages Vcomp (x-axis), with varyingion intensity (abundance) represented in varying colors, according to anillustrative embodiment of the invention. Although, particular colorcoordination may vary, the dispersion plot of FIG. 15A represents thehighest ion intensity in blue with yellow representing the lowest. Thethree-dimensional color dispersion plot 620 represents an aggregation ofdata from a plurality of two-dimensional graphs, such as that shown inFIG. 15B. More specifically, FIG. 15B shows a plot 622 of ion intensity(y-axis) versus Vcomp (x-axis) at a particular Vrf for methylsalicylate. A plurality, illustratively more than two, of such graphstaken at a plurality, illustratively more than two, of field voltagesVrf are aggregated to provide the color plot 620 of FIG. 11A.Aggregating a plurality of scans taken at a plurality of filter fieldvoltages Vrf (and thus, field strengths) provides a more discriminatingscan than a single scan taken at a single Vrf. One reason for this isthat the aggregated scans incorporate the above discussed peak shiftingthat occurs due to the changes in Vrf. As can be seen, thethree-dimensional representation of FIG. 15A provides three signaturepeaks 621, 623, and 625, as opposed to the two peaks 627 and 629 of FIG.15B.

The effect of the increased resolution provided by employing dispersionplots, is even more evident, when trying to distinguish betweencompounds having similar ion mobility characteristics. By way ofexample, FIGS. 16A and 16B show positive mode plots 624 and 626 forDMMP, while FIGS. 17 and 18 show positive mode plots 628 and 630 forDIMP. More specifically, FIGS. 16B and 18, plot ion intensity (y-axis)versus Vcomp (x-axis) at a particular Vrf for DMMP and DIMP,respectively. As shown, both FIGS. 16B and 18 included three peaks ofsimilar magnitude, located at a approximately the same fieldcompensation voltages, and similarly spaced apart. Distinguishingbetween DMMP and DIMP, based solely on the individual plots 626 and 630of FIGS. 16B and 18 is at best unreliable, and at worst impossible.However, referring to FIGS. 16A and 17, the three-dimensional plots 624and 636 are easily visually distinguishable.

More particularly, the DMMP color plot 624 of FIG. 16A shows three clearpeaks 638, 639 and 640, while the DIMP color plot 628 shows four clearpeaks 631, 632, 634 and 636. While the peaks 638, 639 and 640 nearlyoverlay the peaks 631, 634 and 636, the fourth blue peak 632 for DIMP,which is lacking for DMMP, easily distinguishes the DMMP scan from theDIMP scan. Also, the branches 634 and 636 of the color plot 628 arecloser together than the branches 638 and 640 of the color plot 624.Additionally, the color distribution (e.g., saturation) throughout thebranches of the three-dimensional color plot 624 is not the same as thecolor distribution throughout the branches of the plot 628. As in thecase of previously discussed signature scans, three-dimensionalsignature scans of the type depicted in FIGS. 15A-18 may be stored in alibrary for known compounds. At least portions of one or more of thestored scans may be compared with at least portions of similar scans ofunknown species to identify and generally analyze the unknown species.Any suitable pattern matching approach, including conventional patternmatching approaches, may be employed for such comparison.

It should be noted that although the above discussed dispersion plots ofFIGS. 15A, 16A and 17 employ color changes to indicate intensity,changes in any color-related feature, such as changes in colorsaturation, gray scale or black and white may be employed instead or incombination. Additionally, in a further illustrative embodiment, theinvention generates a curve circumscribing the intensity peaks, and thecolor-related information may be discarded. By way of example, in thisillustrative embodiment, the outlines, for example, for the intensitypeaks 632, 634 and 636 would remain, without the color-relatedinformation. Removing the color-related information provides atwo-dimensional dispersion representation of, for example, Vrf versusVcomp that also takes into account the spectral information gained fromaggregating a plurality of Vcomp scans at a plurality of Vrf values. Anyor all of this two-dimensional information may be incorporated into theabove discussed signature information.

As described above, various illustrative comparison approaches mayemploy pattern matching using, for example, the above described two-and/or three-dimensional dispersion plots. However, in otherillustrative embodiments, the information provided by the dispersionplots is stored in the library as mathematical relationships, andsuitable conventional approaches for comparing such mathematicalrelationships are employed to identify the unknown species.

According to another illustrative embodiment, Vcomp may be plotted onthe x-axis, Vrf on the y-axis, and ion intensity on the z-axis. Thus,instead of showing ion intensity as color, saturation, gray scale orblack and white variations, as in the three-dimensional color plots 620,624, and 628, ion intensity may be depicted/conceptualized in atopographical manner. Multi-dimensional signature representations ofthis sort may also be stored in the library of known species and used inthe same fashion as the above described ion mobility signatures. Inother embodiments of the invention, more than three dimensions may beemployed, for example, plotting spectral data as clusters inn-dimensional space and employing known cluster matching algorithms.

A processor, such as the processor 46 of FIG. 5, may be programmed in aconventional fashion to automatically step an analyzer, such as thesystem 10, through a range of field voltages Vrf and a scanned Vcomp,and provide the data to a display or other system for processing andgeneration of a three-dimensional dispersion plot.

Another analysis improving effect can be observed with the applicationof relatively high field strengths. Specifically, complex ion groupingscan be fragmented, for example, by applying a high field strength to thesample. Sample fragmentation is a useful technique for enhancing speciesseparation, detection, and identification. Fragmentation includes aprocess in which large molecules of samples are broken up into smallermolecules, components, or fragments prior to sample detection. Thisenables the components of the group to be individually detected and moregenerally analyzed.

FIG. 19 is an example of such an effect on a mercaptan sample. Inparticular, a range of background voltages (from 620-1450 Vpeak) wereapplied to an ethyl mercaptan spectra in which a general shift of ionpeak behavior can be seen as electric field conditions are strengthened.However, a fragmentation condition can also be observed. Specifically,at lower applied field conditions, strong single peak is observed, suchas at 701-1. However, as electric field strength is increased, multiplepeaks 701-n, 702, . . . 710 are observed in a spectra. By observing andrecording the peak locations, not only at the low voltage fieldconditions, but also at a range of field conditions, this fragmentationbehavior can be further exploited to better identify compounds.According to one feature, data indicating the peak RF voltage at whichfragmentation occurs is incorporated into the stored spectral signaturesfor the known samples. According to another feature, the locations ofthe fragment peaks are also or instead incorporated into the storedspectral signatures for further use for matching detection data withknown data.

FIG. 20A is a graph 712 of ion intensity (y-axis) versus fieldcompensation voltage Vcomp (x-axis) illustrating the separation ofdetection peaks at different compensation voltages between light andheavy molecules according to an illustrative embodiment of theinvention. The graph 712 shows that light molecules associated with theRIP background peak 714 may be identified at an arbitrary −30 Vdccompensation voltage, while heavier molecules tend to be clustered andform a peak 716 at about 0 Vdc compensation. By fragmenting a sample ofheavy molecules and detecting the fragments using, for example, a DMS orIMS system, a plurality of ion intensity peaks, each associated with afragment, may be used to create a unique signature of the sample toenable subsequent identification of that sample. Fragmentation of asample may be achieved, for example and without limitation, by using anyone or a combination of a chemical reaction, a high energy field at highstrength, high field voltage, heating, laser light, colliding the samplemolecules with other molecules, soft x-ray, or the like.

FIG. 20B is a graph 718 of ion intensity (y-axis) versus fieldcompensation voltage (x-axis) showing the increase in number of peaksdetected after sample fragmentation according to an illustrativeembodiment of the invention. The graph 718 shows that fragments arelighter, and therefore, have lower mass and higher associatedcompensation voltages, resulting in improved resolution of anddifferentiation between the fragments. Also, the graph 718 shows anincreased number of peaks 720 associated with the fragmented sample,which increases the collective data that may be used to fingerprint thecompound. The additional detection data enable a more accurateidentification of the detected species, such as by comparing thesignature detected with a set of signatures in a look up table and byother techniques disclosed herein.

FIG. 21 is a conceptual block diagram of a dual channel detection system748 including a first DMS system 722 using fragmentation and forming afirst channel operating in parallel with a second DMS system 724 notusing fragmentation and forming a second channel to improve sampleanalysis according to an illustrative embodiment of the invention. Asshown, the DMS system 724 includes a sample inlet 726, ionization region728, ion source 730, analyzer region 732, and outlet 734. Similarly, theDMS system 722 includes a sample inlet 736, ionization region 738, ionsource 740, analyzer region 742, and outlet 744. The DMS system 722,however, also includes a fragmentation energy source 746 within theionization region 738. The analyzer regions 732 and 742, respectively,include a DMS filter and detector to enable detection and identificationof samples. In operation, the dual channel detection system 748 operatesDMS systems 722 and 724 concurrently, simultaneously or alternatively.With respect to the DMS system 724, a sample S is introduced intoionization region 728 via the sample inlet 726. The ionization source730 may then ionize the sample S into positive and/or negative ions thatare then delivered to the analyzer region 732. The analyzer region 732performs filtering and detection of the sample which then exits the DMSsystem 724 via the outlet 734. The DMS system 722 operates in a similarmanner as the DMS system 724, but with an additional fragmentationsource 746. Thus, when the sample S enters ionization region 738 of DMSsystem 724, the fragmentation source 746 breaks up/fragments the sampleS molecules into lighter, less massive molecules. These lightermolecules are then delivered to analyzer region 742 for filtering anddetection.

Thus, the dual channel detection system 748 using DMS systems 722 and724 may improve sample analysis by substantially simultaneouslyanalyzing a sample S and its fragments to create a more completesignature of the sample. Alternatively, the dual channel detectionsystem 748 may selectively compare the fragmentation spectra, dependingon the sample species to be detected and the need for betterdiscrimination from other interferants or compounds.

FIG. 22 is a conceptual diagram of a DMS system 750, not usingfragmentation, and operating in series with a DMS system 752 usingfragmentation to improve sample analysis according to an illustrativeembodiment of the invention. The combination of the DMS systems 750 and752 form a serial detection system 754. As shown, the serial detectionsystem 754 includes a sample inlet 756, the DMS system 750, the DMSsystem 752, and an outlet 758. The DMS system 750 includes an ionizationregion 760, ion source 762, ion filter 764, and detector 766. The DMSsystem 752 includes an ionization region 768, ion source 770,fragmentation source 772, ion filter 774, and detector 776.

In operation, a sample S is introduced into the serial detection system754 via the sample inlet 756. The DMS system 750 ionizes the sample Susing the ionization source 762 within the ionization region 760. Then,the ionized sample S is delivered to the ion filter 764. The ion filter764 applies a combination of field and field compensation voltage to thesample S to allow selected ion species to reach and be detected by thedetector 766.

FIG. 23A is a graph 778 of ion intensity (y-axis) versus Vcomp (x-axis)showing peak detection for the DMS system 750. As shown previously, whenno fragmentation occurs, the relatively heavy sample molecules clusterto form a peak 780 at Vcomp=approximately 0 Vdc.

After analysis by the DMS system 750, the sample S is delivered to theDMS system 752, where the sample S is ionized by an ionization source770, and also fragmented by the fragmentation source 772. Thefragmentation source 772 may be a radioactive source, a high energyvoltage source or the like with enough energy to break up the relativelylarge sample molecule into a plurality of fragment molecules, fragments,components, or atoms. Then, the fragments are delivered to the ionfilter 774 whereupon a combination of filter field voltages Vrf andfield compensation voltages Vcomp applied a plurality of filter fieldconditions to the fragments to filter them before detection by thedetector 776.

FIG. 23B is a graph 782 of ion intensity versus compensation voltageshowing peak detection for the DMS system 752 of FIG. 22 usingfragmentation. As shown previously, when fragmentation occurs, therelatively lighter fragments form a plurality of ion intensity peaks 784at various distinct field compensation voltages Vcomp.

Thus, the serial detection system 754 using the DMS systems 750 and 752may improve sample analysis by serially detecting a sample S and itsfragments to create a more complete signature or fingerprint of thesample. Alternatively, the serial detection system 754 may selectivelycompare the fragmentation spectra depending on the sample species to bedetected and the need for better discrimination from other interferantsor compounds.

FIG. 24 is a conceptual block diagram of a DMS system 786 including afragmentation region 792 according to an illustrative embodiment of theinvention. As shown, the DMS system 786 includes a sample introductionregion 788, ionization region 790, fragmentation region 792,fragmentation source 806, fragmentation effluent inlet 794, transporteffluent inlet 796, ion filter 798, detector 800, and controller 812. Anionization source 802 may optionally be located within the fragmentationregion 792. An ionization source 804 may optionally be located withinion filter 798.

In operation, a sample S is introduced into sample introduction region788. The sample introduction region 788 may perform pre-separation ofthe sample S to reduce the amount of interferants or unwanted compounds.The ionization source 808 then ionizes the sample S in the ionizationregion 790. Once the sample S is delivered to the fragmentation region792, the fragmentation source 806 fragments the relatively heavymolecules of the sample S into a plurality of lighter fragments.Alternatively, a fragmentation gas including fragmentation molecules maybe introduced into fragmentation region 792 via fragmentation gas inlet794. The fragmentation gas molecules, upon colliding with the sample Smolecules, cause a portion of the sample S molecules to break up intosample S fragments.

After fragmentation, a transport effluent, such as a carrier gas CG maybe introduced via the transport effluent inlet 796 to deliver the sampleS fragments to the ion filter 798. After filtering, the fragments arethen detected by the detector 800. The ionization source 802 mayoptionally be located in the fragmentation region 792. Furthermore, asin the case of all of the previously described illustrative embodiments,the fragmentation source 806 may function additionally as a ionizationsource. The ionization source 804 may optionally be located in the ionfilter 798. Furthermore, the ion filter 798 may also act as either afragmentation source 810 or an ionization source 804.

It should be noted that although the previously described embodimentsrefer to separate ionization and fragmentation sources, in otherillustrative embodiments, a single source may attend to bothfragmentation and ionization. Additionally, any of the previouslydescribed fragmentation approaches may be employed in addition to or inreplacement of the fragmentation sources of FIGS. 21, 22 and 24. Thecontroller 821 may switch fragmentation on and off as needed byactivating or deactivating the fragmentation source 806 or byintroducing or not introducing a fragmentation effluent viafragmentation effluent inlet 794.

The foregoing fragmentation techniques and system implementing thesefragmentation techniques may be used to enhance the detection of asample S, such as without limitation, Sarin gas, also known as:

-   -   GB    -   Zarin    -   Phosphonofluoridic acid, methyl-, isopropyl ester    -   Phosphonofluoridic acid, methyl-, 1-methylethyl ester    -   Isopropyl methylphosphonofluoridate    -   Isopropyl ester of methylphosphonofluoridic acid    -   Methylisoproposfluorophosphine oxide    -   Isopropyl Methylfluorophosphonate    -   0-Isopropyl Methylisopropoxfluorophosphine oxide    -   0-Isopropyl Methylphosphonofluoridate    -   Methylfluorophosphonic acid, isopropyl ester    -   Isoproposymethylphosphonyl fluoride

Sarin, a colorless and odorless gas, has a lethal dose of 0.5 milligramfor an adult. It is 26 times more deadly than cyanide gas and is 20times more lethal than potassium cyanide. Just 0.01 milligram perkilogram of body weight in a pinprick sized droplet will kill a human.

FIG. 25 is a three-dimensional color dispersion plot 814 of the typedescribed above with respect to FIGS. 15A-18 and illustrating detectionof agent GA over a range of field voltages Vrf and field compensationvoltages Vcomp with varying ion intensity presented in varying coloraccording to an illustrative embodiment of the invention. The colordispersion plot 814 includes branches 816, 818, 820, and 822 thatrepresent the detection of fragments of agent GA using, for example, DMSsystem 786 having a Ni⁶³ ionization source for fragmentation of the GAsample at 0.14 ng/l. The branch 840 represents an original peak beforefragmentation.

FIGS. 26A-26H depict two-dimensional graphs 824, 826, 828, 830, 832,834, 836, and 838 of ion intensity (y-axis) versus Vcomp (x-axis), eachat a particular Vrf. As described above with respect to FIGS. 15A-18,the two-dimensional graphs 824, 826, 828, 830, 832, 834, 836, and 838are aggregated into the three-dimensional color dispersion plot 814 ofFIG. 25. As discussed previously, the color dispersion plot 814 improvesthe analysis process of a particular species such as agent GA or GB, forexample, because it takes into account peak shifts due to changes inVrf, and because the color nature of the three-dimensional dispersionplot 814 makes more evident the signature behavior of particular ionspecies in relation to other ion species, especially afterfragmentation.

As described above with respect to FIGS. 15A, 16A, and 17, thedispersion plot of FIG. 25, may employ color saturation, gray scalevariations, black and white variations and/or peak outlines in place ofthe color variations depicted.

The fragmentation techniques described herein are not limited to DMSsystems and may be employed with other mobility-based detection systemssuch as ion mobility spectrometry (IMS), time of flight (TOF) IMS, gaschromatography (GC), Fourier transform infrared (FTIR) spectroscopy,mass spectrometry (MS), liquid chromatography mass spectrometry (LCMS),surface acoustic wave (SAW) sensors, and the like.

Another technique for improving ion species detection, identificationand analysis generally is operating the mobility-based detection system,such as any of the systems described herein, below atmospheric pressure.By operation below atmospheric pressure, the separation between ionintensity detection peaks is increased and the width of the peaks isnarrowed. This provides improved resolution, resulting in improvedsystem discrimination and sensitivity. By operating, for example a DMSsystem at various pressure conditions, the change in ion speciesbehavior with respect to pressure may be measured and used as anothercharacteristic for identifying ion species. According to variousillustrative embodiments, the invention performs ion scans at pressuresbetween about 0.2 and about 0.9 atmospheres, less than about 0.3atmospheres, less than about 0.4 atmospheres, less than about 0.5atmospheres, less than about 0.6 atmospheres, less than about 0.7atmospheres, or less than about 0.8 atmospheres.

FIG. 27A is a graph 840 of background (RIP) ion intensity versus fieldcompensation voltage at a plurality of pressures for a DMS system inpositive ion detection mode according to an illustrative embodiment ofthe invention. The graph 840 shows that the field voltage may beadjusted to maintain the ion intensity peak within the same compensationvoltage position as the pressure within a DMS system is adjusted. Morespecifically, according to the graph 840, as the pressure decreases, thefield voltage decreases to maintain the ion intensity peak for a speciesat the same compensation voltage. Furthermore, changes in pressure atlower pressures result in the need for greater changes in field voltageto maintain a constant compensation voltage. For example, when reducingthe pressure by approximately 100 mmHg from 760 mmHg to 655 mmHg, thereduction in field voltage is approximately 40 Vpeak from about 1050Vpeak to about 1010 Vpeak. For approximately the same pressure reductionfrom 655 mmHg to 556 mmHg, the reduction in Vrf is approximately 90volts from about 1100 Vpeak to about 920 Vpeak. Thus, the field voltagedecrease is approximately twice as great for changes in pressure in the600 mmHg range, which indicates that the resolution is improved atreduced pressure.

FIG. 27B is a graph 842 of background (RIP) ion intensity versus fieldcompensation voltage at a plurality of pressures for a DMS system innegative ion detection mode according to an illustrative embodiment ofthe invention. Like positive mode graph 840, the graph 842 shows that,in negative detection mode, the field voltage may be adjusted tomaintain the ion intensity peak within the same compensation voltageposition as the pressure within a DMS system is adjusted.

As shown by comparing the graph 840 with the graph 842, there is anoffset in the ion intensity peak between the positive mode ion intensitypeaks of graph 840 and negative mode ion intensity peaks of graph 842 atthe same pressure and field voltage. This offset may indicate adifference in the alpha parameter between positive and negative modedetection for an ion species. The alpha parameter is discussed infurther detail below. The DMS flow rate is approximately 300 cc/min ingraphs 840 and 842.

FIGS. 28A and 28B depict graphs 844 and 846, respectively, of ionintensity (y-axis) versus pressure (x-axis) showing a quantifiableeffect on positive and negative background spectra, respectively, causedby a decrease in pressure according to an illustrative embodiment of theinvention. More specifically, the graph 844 shows that field voltage isdecreased by about 50% when pressure is decreased to about 0.3atmosphere (atm). The graph 846 also shows a similar field voltagedecrease of about 50% when pressure is decreased to about 0.3 atm.

FIGS. 29A and 29B depict graphs 848 and 850, respectively, showing ionintensity (y-axis) versus field compensation voltage (x-axis) for aplurality of pressures and showing the effect of varying pressure onnegative and positive tert-butylmercaptan and tert-butylithiol (TBM)spectra, respectively. While the graphs 848 and 850 show that fieldvoltage decreases as pressures decrease for a particular fieldcompensation voltage, the graphs 848 and 850 also show that the ionintensity peak positions for TBM spectra shift in the opposite directionas the ion intensity peak shifts for the background (RIP) spectra ofgraphs 840 and 842. Furthermore, the level of change of the ionintensity peaks in graphs 848 and 850 for TBM spectra is less than thelevel of change of the ion intensity peaks in graphs 840 and 842 forbackground spectra.

FIGS. 30A and 30B depict graphs 852 and 854 showing ion intensity(y-axis) versus pressure (x-axis) and showing the effect of varyingpressure on negative and positive TBM ion peak parameters, respectively.More specifically, the graph 852 shows that the ion intensity peakremains relatively constant as the pressure is varied for negative ionspectra. The graph 854 shows that the ion intensity peak remainsrelatively constant with the level decreasing slightly at a lowerpressure for positive spectra. Because changes in pressure impact thebackground (RIP) and analyte spectra differently, pressure may bemanipulated, regulated, or otherwise controlled in such a manner as toimprove the ability of a DMS system to detect and identify ion specieswith better resolution while minimizing the negative effects ofbackground spectra interference.

In certain embodiments, it may be desirable to maintain uniformdetection results by maintaining a constant ratio of electric fieldstrength to gas density N or pressure P where the ratio is expressed asE/N or E/P. Thus, when the gas operating pressure within a DMS system isdecreased, the field voltage is correspondingly lowered to maintain aconstant E/N or E/P. This reduction in field voltage results in areduction in power consumption which, in turn, results in smaller,lighter weight, and lower cost detection systems.

FIG. 31 is a graph 856 showing the effect of reduced pressure on analytepeaks for chemical warfare agents, such as DMMP, DIMP, and MS. The topgraph 857 shows the ion intensity results at atmospheric pressure, whilethe bottom two graphs 859 and 861 show the results at 0.65 and 0.5 atm,respectively. At 1 atm with field voltage at Vrf=about 1000 Vpeak, thetop spectra shows the overlap 858 of monomer and dimmer cluster peaksfor DIMP over a range of about 10 Vdc field compensation voltage. But at0.65 atm and Vrf=about 800 Vpeak, the monomer peak 860 and cluster peak862 are separated with the monomer peak 860 at Vcomp=about −3 Vdc andcluster peak 862 at Vcomp=about +1 volt. At 0.5 atm and Vrf=about 650Vpeak, the DIMP monomer peak 864 and DIMP cluster peak 866 are eachnarrower with the peaks 864 and 866 at Vcomp=about −2.5 Vdc and about +1Vdc, respectively. The narrower peaks 864 and 866 at 0.5 atm result inhigher resolution for a DMS system.

FIGS. 32A-32D depict graphs 868, 870, 872, and 874, respectively,showing ion intensity (y-axis) versus Vcomp (x-axis). The graphs 868,870, 872 and 874 show improved detection resolution for agent GF atreduced pressures, according to an illustrative embodiment of theinvention. The graphs 868 and 870 show the ion intensity spectra ofagent GF at Vrf of 1500 and 1000 Vpeak, respectively, at 1 atm. Thegraphs 872 and 874 show the ion intensity spectra of agent GF at Vrf of1000 and 750 Vpeak, respectively, at 0.5 atm. According to the graph870, the monomer and dimer peaks overlap at peak 876 at Vrf=about 1000Vpeak. According to the graph 868, however, the monomer peak 878 anddimer peak 880 are separated at Vrf=about 1500 Vpeak. Thus, DMS systemresolution may be increased by increasing the field voltage (Vrf).

In the graph 872, the DMS system pressure is reduced to about 0.5 atmwith Vrf at about 1000 Vpeak. The graph 872 shows the monomer peak 882clearly isolated from any dimer peak, because the cluster or dimer RIPpeaks are off-scale of the graph 872. In the graph 874, the fieldvoltage Vrf is reduced to about 750 Vpeak, with a system pressure atabout 0.5 atm. The graph 874 shows clear separation of the GF monomerpeak 884 from the dimer peaks 886 and RIP peak 888. Thus, GF may bedetected and identified by the signature peaks illustrated in graph 874in a DMS system utilizing reduced pressure, reduced field voltage, and,therefore, reduced power.

As described above, three-dimensional color dispersion plots may be usedto significantly enhance the ability of a DMS system to detect andidentify ion species of interest by allowing a user or patternrecognition program to match the color patterns against a library ofsimilar color pattern for known compounds.

FIG. 33 is a three-dimensional color dispersion plot 890 depictingintensity of positive ions of 0.005 mg/m³ DIMP at about 0.65 atm andover a range of field strengths, gas densities (E/N) and fieldcompensation voltages Vcomp. As shown, gas density is plotted on thex-axis, Vcomp is plotted on the y-axis, and variations in intensitydepicted by variations in color. The plot 890 includes several prominentbranches 892, 894, and 896.

FIG. 34 plots the same information as FIG. 33, except as obtained at adecreased pressure of about 0.50 atm. As shown in plot 898, thereduction in pressure in relation to plot 890 results in significantlymore prominent branches 900, 902, and 904, thus providing enhancedresolution.

FIG. 35 is a graph depicting positive (906) and negative (908) modethree-dimensional color dispersion plots for about 0.85 mg/m³ of agentGB RIP, at a relative humidity (RH)=about 87%, in a DMS system operatingat about 0.5 atm for a fragmented sample. The negative mode plot 908shows only a single strong RIP branch 909, while the positive mode plot906 shows two strong trace analyte peaks 901 and 903 to the right of theheavy background RIP branch 905. Thus, plotting three-dimensional graphsfor both the positive and negative ion species of a sample providesfurther enhanced ion species identification over three-dimensional plotsof positive or negative mode measurements alone.

The three-dimensional color dispersion plots 906 and 908, as illustratedabove, may also show discontinuities in the branches, i.e., peak plotsor traces, that are also useful for species identification. For example,the plot 906 includes a break in the trace or branch 901 that may beincluded as part of the stored signature for future comparisons.

As described above with respect to FIGS. 15A, 16A, 17 and 25, thedispersion plots of FIGS. 33 and 35, may employ color saturation, grayscale variations, black and white variations and/or peak outlines inplace of the color variations depicted.

According to another feature, the identification above describedanalysis approaches may be made device-independent. FIGS. 36A and 36Bshow experimental detection data for a homologous group of ketones,including: acetone, butanone, pentanone, hexanone, heptanone, octanone,nonanone, decanone. FIGS. 37 and 38 are tables showing monomers andclusters, respectively, for the above listed keytone species. As shownin FIGS. 36A and 36B, each species has a unique mobility curve, and thusa unique mobility signature, for the given set of field conditions. Asdescribed above, the mobility signatures may be obtained and enhanced inany of a plurality of ways. However, the identification process can befurther enhanced by making it device-independent. With deviceindependence, signature data can be created that can be used on anydevice. According to one illustrative embodiment, the inventionaccomplishes this by determining the parameters of a function derivedfrom the fundamental mobility coefficient associated with each species.

Therefore, for example, the multiple data represented in FIGS. 36A, 36B,37 and 48 each can be used to provide positive identification of adetected species by the unique and inherent mobility characteristic thatidentifies that species. According to one feature, the comparison can bemade to a lookup library specific to the device in question, but alsocan be made to a universal set of data that is device-independent. Thus,in general, one does not wish to only compare the plot of abundancecurves versus compensation voltage individually, but rather generate aplot of observed peak locations for specific compensation voltages, sothat curves, slopes, signs, and various details can be discerned foreach of the detected ions for comparison to a library of lookup data.

More specifically, in computing mobility signatures, we have found thatan expression of the field-dependence of ion mobility, the so-called αcoefficient, expressed as a function of field, can be used to generate aunique α function that is inherent for that species and is deviceindependent. Thus the α function can be used as the unique signature ofa species; this function expresses both a characteristic signature forthe ion species and is device independent. In short, according to onefeature, the invention recognizes that peaks change position insignature ways because they have different alpha signatures.

In one illustrative embodiment, the invention employs the α function asa mobility signature for detected species. The signature can bedetermined for a detected unknown compound, based on the fieldconditions that are used, and then this can be used to make anidentification according to a lookup table of stored known signaturedata associated with known compounds. More particularly, in practice ofa preferred embodiment of the invention, ion species are identifiedbased on the mobility dependence of the species under various fieldconditions. Data is collected for the sample under test for at least twofield conditions, the data is processed, and a comparison of detectiondata computed as an α function for the sample under test versus thestored data enables identification of the compounds in the sample.

Referring again to the discussion of the α parameter, FIG. 3 is a plotof mobility versus electric field strength for three examples of ions,with field dependent mobility (expressed as the coefficient of highfield mobility, α) shown for species at α greater, equal to and lessthan zero. For any given set of field conditions, the field strength andcompensation can be correlated with an α value. This is shown in thework of Buryakov et. al., A New Method Of Separation Of Multi-AtomicIons By Mobility At Atmospheric Pressure Using A High-FrequencyAmplitude Asymmetric Strong Electric Field, Intl J. MassSpec and IonProc. (1993), at p. 145.

We have observed that knowing the α parameter alone at a particularfield strength does not prevent false positives. This would occur at theintersection of the two plots in FIG. 4, at the point indicated byreference numeral 100. Without more information, knowledge of the αparameter for the respective ion species at that location does notprovide unique mobility signatures for both compounds. Thus, withoutdoing more, any number of readings at this intersection is likely toresult in a detection error.

However, we have also found that we can express an ion's α mobilitycharacteristic as a function of field, i.e., as α(E), and can define aunique mobility signature for the ion species which isdevice-independent. This α(E) or “alpha function” relates the size,effective cross-section, shape, and mass of the ion to field conditions.It is understood that as the applied electric field increases, theincreasing electric field tends to displace, stretch, and/or break thebonds of the ion such that the stronger the field, the greater theinduced dipole, quadripole, or higher order moments of the ion. These,in turn, affect the relative mobility of the specific ion. The result ofrelating these aspects is to define a unique mobility signature for theion species of interest. This also turns out to be device-independent.

The relationship of the α(E) function to field conditions is shown inthe following:

$\begin{matrix}{{V_{c}(E)} = \frac{\langle{\alpha \; E_{s}{f(t)}}\rangle}{1 + {\langle\alpha\rangle} + {\langle{\frac{\alpha}{E}E_{s}{f(t)}}\rangle}}} & (1)\end{matrix}$

where: Vcomp (peak position); Es-electric field strength; ƒ(t)-waveformparameters (wave shape and so forth).

Thus, for each spectral detection, we can compute α as a function offield conditions, i.e., α(E). Specifically, the asymmetric waveform in aplanar field asymmetric waveform mobility spectrometer,E_(max)(t)=E_(max)ƒ(t), is designed to satisfy the following conditions:

$\begin{matrix}{{{1/T}{\int_{0}^{T}{{E_{s}(t)}\ {t}}}} = {{\langle{E_{s}{f(t)}}\rangle} = 0}} & \left( {3a} \right)\end{matrix}$<ƒ^(2n+1)(t)>≠0  (3b)

where ƒ(t)—is a normalized function which describes the waveform, andE_(max) is the maximum amplitude of the waveform. The waveform isdesigned such that its average value is zero (equation 3a) while thepolarity of the electric field during one period is both positive andnegative. The addition of the compensation field, C, to the waveformE_(S)(t) yields Equation 4:

E(t)=E _(s)(t)+C=E _(s)ƒ(t)+C  (4)

so the average ion velocity over a period of the asymmetric waveform canbe written as:

V=<V(t)>=<K(E)E(t)>  (5)

Only ions with average velocity of zero, v=0, will pass through the gapwithout neutralization. An expression for the compensation fieldrequired to enable an ion to pass through the gap can be obtained bysubstituting Equations 2, 3, and 4 into Equation 5 as shown in Equation6:

$\begin{matrix}{C = {\frac{\langle{\alpha \; E_{s}{f(t)}}\rangle}{1 + {\langle{\alpha.}\rangle} + {\langle{\frac{\alpha}{E}E_{s}{f(t)}}\rangle}}.}} & (6)\end{matrix}$

The value of this compensation electric field can be predicted preciselywhen the alpha parameter for the ion species, the waveform ƒ(t), and theamplitude of the asymmetric waveform E_(max) are known.

A procedure for extraction of α(E) from experimental measurements of theelectric field dependence of the mobility scans is thus known. In thissection, some additional considerations regarding the alpha parameterand methods to determine this parameter are described. First, emphasismust be given that the alpha parameter is a function (not a number) andthe physical and chemical information about an ion is contained in theshape of the α(E) curve. The method of representing this curve isincidental to the topic. The only criterion critical in these methods isthat the calculated values for mobility (i.e. K(E)=K_(o{)1+α(E)]) shouldbe as close as possible to the experimental values. The function forα(E) can be represented as an even power series or in complex form. Ineither instance, the curves of experimental results and calculationsshould agree closely. Thus, the quality of the approximation is limitedby the accuracy of the experimental results and has been illustrated.Discerning the quality of a model based upon two parameters, threeparameters, or a nonlinear function with five parameters was difficult.All approximations were located within the error of ΔC₁ (at ±9%).

In this work, a simple uniform method is described to represent thefunction of α(E), which will be suitable for comparison of resultsobtained under different experimental conditions. These methods could beused for differing asymmetric waveforms or different designs of IMSdrift tubes: linear, cylindrical, or planar DMS. In general then, thecriteria for choosing the level of approximation of alpha is first toensure that the method of extracting the alpha parameter uses the leastnumber of individual parameters of the experimental device. Second, theresult should contain the fewest number of adjustable parameters, andthe approximation curves should be within the experimental error bars.In the next section, the general method to extract the alpha parameteris described and then applied in the subsequent section.

The function of α(E) can be given as a polynomial expansion into aseries of electric field strength E degrees as shown in Equation 7:

$\begin{matrix}{{\alpha (E)} = {\sum\limits_{n = 1}^{\infty}\; {\alpha_{2n} \cdot E^{2n}}}} & (7)\end{matrix}$

Substituting Equation 7 into Equation 6 provides a value of thecompensation voltage as shown in Equation 8 where an uneven polynomialfunction is divided by an even polynomial function. Therefore an odddegree polynomial is placed after the identity sign to approximateexperimental results:

$\begin{matrix}{C = {\frac{\sum\limits_{n = 1}^{\infty}\; {\alpha_{2n}S^{{2n} + 1}{\langle{f^{{2n} + 1}(t)}\rangle}}}{1 + {\sum\limits_{n = 1}^{\infty}{\left( {{2n} + 1} \right)\alpha_{2n}S^{2n}{\langle{f^{2n}(t)}\rangle}}}} \equiv {\sum\limits_{n = 1}^{\infty}{c_{{2n} + 1}S^{{2n} + 1}{\langle f^{{2n} + 1}\rangle}}}}} & (8)\end{matrix}$

This allows the a comparison of the expected coefficient (approximated)to be compared to the values of alpha parameter as shown in Equation 9:

$\begin{matrix}{c_{{2n} + 1} = {{\alpha_{2n}{\langle f^{{2n} + 1}\rangle}} - {\sum\limits_{k = 1}^{n - 1}{\left( {{2\left( {n - k} \right)} + 1} \right)c_{{2k} + 1}\alpha_{2{({n - k})}}{\langle f^{2{({n - k})}}\rangle}}}}} & (9)\end{matrix}$

Alternatively, alpha parameters can be calculated by inverting theformula by using an approximation of the experimental results perEquation 10:

$\begin{matrix}{\alpha_{2n} = {\frac{1}{\langle f^{{2n} + 1}\rangle}\left\{ {c_{{2n} + 1} + {\sum\limits_{k = 1}^{n - 1}{\left( {{2\left( {n - k} \right)} + 1} \right)c_{{2k} + 1}\alpha_{2{({n - k})}}{\langle f^{2{({n - k})}}\rangle}}}} \right\}}} & (10)\end{matrix}$

Any number of polynomial terms (say 2n), in principle, can be determinedfrom Equation 10 though a practical limit exists as the number ofpolynomial terms in the experimental result of the approximation c₂₊₁should be higher than the expected number of alpha coefficients α_(2n).Since the size of n depends on the experimental error, the power of theapproximation of the experimental curves C(E_(s)) cannot be increasedwithout limit. Usually N experimental points of C_(i)(E_(si)) exist forthe same ion species and experimental data can be approximated by thepolynomial using a conventional least-square method. Finally, the numberseries terms cannot exceed the number of experimental points soincreasing the number of series terms above the point where the fittedcurves are located within the experimental error bars is unreasonable.In practice, two or three terms are sufficient to provide a goodapproximation shown in prior findings. The error in measurements must bedetermined in order to gauge the order of a polynomial for alpha. Thesources of error in these experiments (with known or estimated error)were:

-   -   1. Error associated with measurement and modeling of the        RF-field amplitude (˜5%);    -   2. Error in C(E_(s)) from a first-order approximation of        Equation 4 (˜3%), and    -   3. Error in measuring the compensation voltage (˜5-8%).        An approximate error may be ˜10% and there is no gain with        approximations beyond two polynomial terms; thus, alpha can be        expressed as

α(E/N)=1+α₁(E/N)²+α₂(E/N)⁴ with a level of accuracy as good as permittedby the measurements.

A standard least-square method (regression analysis) was used toapproximate or model the experimental findings. For N experimentalpoints with C_(i)(E_(si)) and for C=c₃S³+c₅S⁵ a function y=c₃+c₅x can bedefined where y=C/S³; x=S² so c₅ and c₃ are given by Equations 11 and12, respectively:

$\begin{matrix}{c_{5} = \frac{{\sum\limits_{i = 1}^{N}{x_{i}{\sum\limits_{i = 1}^{N}y_{i}}}} - {N{\sum\limits_{i = 1}^{N}{x_{i}y_{i}}}}}{\left( {\sum\limits_{i = 1}^{N}x_{i}} \right)^{2} - {N{\sum\limits_{i = 1}^{N}x_{i}}}}} & (11) \\{c_{3} = {\frac{1}{N}\left( {{\sum\limits_{i = 1}^{N}y_{i}} - {c_{5}{\sum\limits_{i = 1}^{N}x_{i}}}} \right)}} & (12)\end{matrix}$

Through substituting experimental value c₃, c₅, values for α₂ and α₄ canbe found per Equations 13 and 14:

$\begin{matrix}{\alpha_{2} = {c_{3}/{\langle f^{3}\rangle}}} & (13) \\{\alpha_{2} = \frac{c_{5} + {3c_{3}\alpha_{2}{\langle f^{2}\rangle}}}{\langle f^{5}\rangle}} & (14)\end{matrix}$

In order to calculate α_(2n), knowledge is needed for the approximationsof experimental curves for C(E_(s)) and for the function ƒ(t)—which is anormalized function describing the asymmetric waveform.

For example, nine data points were identified for each of the eightketones of FIGS. 36A, 36B, 37, and 38, based on the data collected inthe tables of FIGS. 37 and 38. These can be used to compute the α curvefor that species, such as with a piecewise linear approximation to the αcurve. For example, two data points for butanone are a(Vcomp-a, Vrf-a)and b(Vcomp-b, Vrf-b). Between these two points, the slope and sign ofthe butanone curve can be computed. More complete characterization ofthe curve, such as with polynomial curve fitting, is also possible.

Now this data set becomes part of a data store for use in identificationof the species of an unknown detected ion species for which two datapoints are collected and the corresponding curve data is computed. Inshort, in an illustrative practice of the invention, we collect data onat least two closely associated points (peaks) for a given ion sampleand generate the curve data accordingly. Once we have the detected andcomputed data, we assume this approximates the alpha curve and thereforedo a lookup to our stored data. Upon finding a match, we can thenpositively identify the sample.

In FIGS. 39A and 39B (monomers and clusters, respectively) we computedunique a curves for keytone ions (acetone, butanone, pentanone,hexanone, heptanone, octanone, nonanone, decanone) based on datacollected in the tables of FIGS. 37 and 38, plotting the percent changein a against the change of field strength for the various datacollected. These plots of percent change in a against field strengthexpress a unique signature for each of these ion species. This is loadedin our data store for later comparison: the signature data includes theRF field strength and the compensation voltage at which the peak isdetected. We also associate with it the identifying data for the known αfunction associated with that detected peak location and fieldconditions for each species.

FIGS. 39A and 39B thus express the α function for individual ketonesspanning electric fields of 0 to 80 Td (˜23 kV/cm), expressed as apercentage change in alpha as a function of field conditions. Theseplots are fundamental signature features of these ion species that areindependent of the drift tube parameters and can be used in othermobility spectrometers. Thus, the α function can be favorably used inpractice of the invention to provide a mobility identification data setthat is device-independent.

These results are surprising and demonstrate that for chemicals with thesame functional group, protonated monomers of a single type exhibit abroad range of behavior vis-à-vis the dependence of coefficients ofmobility on electric fields. This difference in behavior for a commonmoiety suggests that the effect from the electric field must beassociated with other aspects of molecular structure. One possibleinterpretation is that ions are heated during the high field and theeffect on the protonated monomer should be striking These ions withstructures of (H₃O)⁺M (H₂O)_(n) or perhaps (H₃O)⁺M (H₂O)_(n)(N₂)₂,should be prone to dissociations with slight increases in iontemperature caused by the high field conditions. Thus, ioncross-sections and mobilities would accompany declustered small ions athigh fields.

Referring again to FIG. 39A, it should be noted that there isapproximately a 20% increase in α(E) for the protonated monomer ofacetone with high fields. As the molecular weight of the keytone isincreased, ion heating is less pronounced and reflected in the α(E)function. The α(E) function for proton bound dimers (clusters) isconsistent with decreases in mobility under high field conditions.Consequently, the basis for the α(E) function differs from that ofprotonated monomers. Indeed, the proton bound dimer for decanoneundergoes about a 5% decrease at high fields. The cause for a decreasein mobility at high fields has no existing model but should be due toincreased collisional size or increased strength of interaction betweenthe ion and the supporting gas.

Furthermore, if we were to do the same for the cyclohexane and DMMP inFIG. 4, the computed alpha curves would differ accordingly. In thismanner, the invention can distinguish ion species even when theirmobility curves overlap, as long as we have at least a second detectiondata set to associate with each detected species in question. Therefore,the invention achieves a high level of assurance for the accuracy ofidentifications.

Thus we have shown that the fundamental dependence of mobility for ionsin high electric field can be obtained from field asymmetric ionmobility spectrometry. Functions of dependence can be extracted fromexperiments using known methods to treat imperfect waveforms. Thesefindings show an internal consistency with a homologous series ofketones, and also indicates a mass dependence not previously reported.

Focusing attention now on FIGS. 40A-40F a specific sequence of steps isdescribed that may be carried out to perform species identification inseveral of the embodiments of the invention. These steps are provided byway of illustration and not limitation. In this illustration, thesequence of steps may be performed by the microprocessor 46 of the ionmobility spectrometer device 10 of FIG. 5. The microprocessor 46provides digital control signals to the RF dispersion voltage (Vrf)generator 42 and compensation voltage (Vcomp) generator 44 to controlthe drive voltages for the filter 24. The voltage generators 42 and 44may also include, for example, digital-to-analog converters, not shownin detail in FIG. 5.

The microprocessor 46 coordinates the application of specific RFdispersion voltages Vrf and compensation voltages Vcomp, also takinginto account the function of observing responses from the detector 26 asread through the analog to digital converter 48. By detecting attributes(such as the peaks) of observed abundances of a particular ion speciesacross a range of Vrf voltages, the microprocessor 46 can thus takesteps to identify particular compounds. These may include, for example,comparing or correlating particular “response curve” data against alibrary of response curve data as stored in the memory 47. They can alsoinclude computation of a curve parameters. The results of the comparisonoperation can be provided in the form of an appropriate output devicesuch as a display or personal computer or the like, or maybe provided byelectrical signals through an interface to other data processingequipment.

As shown more particularly in FIG. 40A, a state 1000 is entered into themicroprocessor 46 in which a compound is to be analyzed. Here, thecompound is known and identified, such as by a user supplying anidentifying text string to the computer. A sequence of steps is thenperformed by which data is to be acquired concerning the known chemicalcompound. From this state 1000, a next state 1002 is entered in which arange of dispersion voltages Vrf and compensation voltages Vcomp aredetermined by the processor 46. These ranges include a beginning voltage(b) and an end voltage (s) and step voltage(s) to be applied to each ofthe ranges Vrf is thus varied from an initial value Vrf(b) to a finalvalue Vrf(e) by a step amount Vrf(s). Similarly, Vcomp is to be variedfrom Vcomp(b) to a final value Vcomp(e) by a step amount Vcomp(s).

The voltage ranges are then applied in the following steps.Specifically, step 1004 is entered in which the Vrf is allowed to stepthrough a range of values. A state 1008 is entered next in which thecompensation voltage Vcomp is also swept or stepped through a series ofvalues or ranges. In state 1010, the response to each applied voltage isstored as a value, (a).

If the last compensation voltage has not yet been tested, thenprocessing returns to state 1008 in which the next compensation voltageis applied. However, in state 1012, if all of the compensation voltageshave been applied, then processing proceeds to a state 1014 wherein atest is made to see if all of the dispersion has been applied.

The loop continues until all of the compensation and dispersion voltageshave been applied. The resulting set of data is then analyzed in a state1018 to identify features of interest. In the specific example beingdescribed, it is the peak locations that are of interest. For each suchpeak in an observed response for a given applied dispersion voltage Vrf,a response value for a specific Vcomp is determined and itscorresponding amplitude (a) is detected and stored.

The response curve data, or certain attributes thereof such as the peaklocations are then stored as a data object P (or table) as shown in FIG.40B. Such an object illustratively contains an identification of thetested compound such as a text string. Also stored are a set of theapplied dispersion voltages Vrf. For each such dispersion voltage Vrf, acorresponding peak compensation voltage is stored. Specifically, atleast the compensation voltage Vcomp at which a peak was observed, andpreferably, the corresponding amplitude of the response (abundance)observed at that peak is stored.

As previously described in detail, for a given Vrf, there may be a setof compensation voltages at which a number of “peaks” are observed. Forexample, as was described in connection with FIG. 14A, the sampleanalyzed can be made up of a compound of specific ions, includingmonomers, cluster ions, and reactant ion peaks. Thus, illustratively,there is an accommodation in the structure of object P to anticipatethat there will be more than one peak observed in any particularmobility scan, and that the number of peaks per response curve may notalways be the same number.

An example, the illustrative object P of FIG. 40B, includes a dataelement, where for a single RF dispersion voltage Vrf-1, peaks may beobserved at compensation voltages Vc11, . . . , Vcmn havingcorresponding amplitudes a11, . . . , amn. This may correspond to thecase of the lowest applied dispersion voltage in FIG. 14A, wherenumerous peaks 601-, 605-1, 608-1 are detected. However, at anotherdispersion voltage Vrf-m, only a single peak at Vcomp-m, am wasdetected. This might correspond to a case such as in the uppermost curveof FIG. 6A, where only a single peak 601-m was detected.

In an illustrative application, a library of data objects P (referencevectors) is developed by performing the steps of FIG. 40A for aplurality of known compounds of interest. This then permits aninstrument to eventually enter a chemical recognition state 1200 asshown in FIG. 40C. Next, a series of measurements are taken in states1202-1214. This series is similar to the measurements taken in FIG. 40A.Specifically, a series of measurements are taken for a specifiedcompensation and RF voltages. It should be understood that an entire setof all of the same measurements need not be taken in this mode as weretaken in the chemical data acquisition mode. Specifically, not allpoints on a relatively dense response curve need to be taken, onlyenough to identify each compound.

Once the measurements are taken, a state 1220 is entered in whichfeatures, such as peaks of the response are identified for each peak, acorresponding compensation voltage and amplitude may be identified, andthese stored to a candidate measurement vector P′. The candidate vectorP′ thus represents a series of data that needs to be tested against anumber of candidate compounds. The candidate vector P′ is then analyzedin states 1230 and/or 1240 by looking up corresponding counterparts inthe library of reference vector objects P, and scoring a match between Pand P′. These steps may be iterated until such time as a match or a bestmatch is determined in a state 1250.

It should be understood that any number of techniques may be used todetermine a degree of match between P and P′. For example, if theelements (Vcomp, a) of P and P′ are considered to be data points inEuclidian geometry space, a distance can be computed. The comparisonwith the smallest Euclidian distance can then be selected as the bestmatch. However, other recognition techniques may be used to determine anidentity of an unknown compound, for example, more sophisticated signalprocessing techniques such as correlation may be used to resolve peaks;or other known pattern recognition algorithms, neural networks orartificial intelligence techniques may be used to find a best match forP′. This best match is then identified to a user, such as by looking upthe compound identifier field and displaying it in state 1260.

FIG. 40D shows a series of steps, which may be added to the dataacquisition phase and the chemical recognition phase to take advantageof second order data processing characteristics. For example, in thedata acquisition state, a series of states 1020, 1022, 1024 and 1026 maybe added to curve-fit specific attributes of the measured response.Specifically, a state 1020 may be entered in which for each data elementof the object P a vector, z, is formed consisting of the peakcompensation voltages vc11, vc12, . . . vc1 m.

This vector is a vector of point locations for the peaks observed for arange of compensation voltages. Returning attention to FIG. 14A,briefly, this may correspond, for example, to locating the points 601-1,. . . 601-m, . . . 601-n corresponding to peak height and locations forthe monomer ions of interest. A curve may then be fit through thesepeaks such as by applying a curve fitting algorithm, in state 1024. Inthe illustrated example it is assumed that a quadratic equation isfitting the peaks of the form y²=βx²+γ. The β and γ coefficients canthen be stored in the state 1026 associated with the vector. Thechemical is thus identified by a curve fit to its peak locationsapproximating its mobility (α coefficient) behavior.

If this is done, a corresponding set of steps 1270, 1272 and 1274 can beadded to the recognition process to identify peaks by performing a curvefit to observe data, and then, determining γ and β coefficients, ratherthan comparing raw data values in states 1270 and 1272. In state 1274,the β and γ coefficients are tested to determine closest matches in theP object library.

FIG. 40F shows a series of steps that may be used to identify ordistinguish peaks in the acquisition phase. Here initial data may beadded to the objects P by identifying peaks as a cluster peak or monomerpeak. Specifically, if a peak shift over a range of field conditionvoltages (e.g., FIG. 14A) increases (i.e., shifts to the right), thenthis may be identified as a cluster peak. If the peak does not meetspecific shifting criteria, it may be identified as a monomer peak.States 1310, 1331, and 1332 may thus be added to the identificationprocess. The results of these steps adds an additional parameter Lassociated with each data point in the object P to further identify eachpeak as a monomer cluster or other peak type, as shown in FIG. 40E.

Other approaches to this may be used to label peaks. For example,reactant ion peaks (RIP) may also be identified by performing ananalysis on a response of the instrument, with no sample S applied. Inthis mode, only the RIPs occur, and in their behavior across a range ofcompensation voltages can be stored. Information concerning theparticular type of peak may be stored in pointer data in a state 1320,at which such a peak is detected. This information can then be added tothe objects P, specifically as shown in FIG. 40E.

FIG. 40G shows additional processing steps, which may be performed inthe compound recognition state to take advantage of the situation ofFIGS. 36A-38 in which monomer and cluster ion behavior is observed.Specifically, the steps of FIG. 40G may be added as further steps 1280in the recognition phase. Here, for every candidate peak P′, acorresponding monomer peak in the reference array P is compared. A scoreis then associated with the closest of the match in state 1284.Similarly, in state 1286, a cluster peak may be compared with itscorresponding peak in the peak library P. A score sc is then determinedin step 1288, depending on the closest of this match. In a state 1290, afinal score sf can be associated with weighting the monomer peak scoreand the cluster peak score by weighting factors wm and wc. For example,in an instance where cluster peaks are expected to provide moreinformation than monomer peaks, cluster peaks may be weighted highly andmonomer peaks relatively low or zero factor. Using this weighting, bothmonomer and cluster peak identification can be combined to furtherrefine compound analysis.

In various applications, the above described approaches to ion-basedsample analysis may be employed in relatively compact, such as handheld,analyzer systems. FIG. 41 is a conceptual diagram of such a compact DMSanalyzer system 1400. The DMS system may be used, for example, toanalyze compounds, such as chemical warfare agents (CWAs), and ToxicIndustrial Compounds (TICs), and Toxic Industrial Materials (TIMs)according to an illustrative embodiment of the invention. By operatingthe compact DMS analyzer system 1400 at less than atmospheric pressure,e.g., 0.5 atm, as described above, the system 1400 approximately doublesits resolution over existing state-of-the-art systems, while reducingits power consumption and size. By performing sample fragmentation, asdescribed above, sample analysis may be further enhanced. By utilizingthree-dimensional color dispersion plots, as also described above,analysis of CWAs, TICs, and TIMs is further enhanced.

The DMS analyzer system 1400 may employ an electromechanical pump,compressed gas or air, or the solid-state flow generator 1402, whichincludes an ion source 1404, an ion attractor 1406, and a constrainedflow channel 1408 for controlling sample flow and/or pressure within thesystem 1400. The ion source 1404 provides a source of ions and the ionattractor 1406 attracts either positive or negative ions, depending onan applied bias voltage. The ion flow created in the constrained channel1408 due to the ion flow generated by the interaction of the ion source1404 with the ion attractor 1406 creates a fluid, e.g., a sampleeffluent, flow. In some illustrative embodiments, the DMS analyzersystem 1400 may be miniaturized, such that the analyzer unit 1410 isincluded in application-specific integrated circuits (ASICs) embedded ona substrate 1412. A solid state flow generator of the type employed bythe invention is described in further detail in co-pending and co-ownedU.S. patent application Ser. No. 10/943,523, filed on 17 Sep. 2004, theentire contents of which are incorporated above by reference.

The constrained channel 1408 includes an inlet end 1414 and an outletend 1416. The constrained channel 1408 also includes a sampleintroduction inlet 1418 to enable the analyzer 1410 to collect thesample gas for analysis. A pre-concentrator 1420 may be employed at thesample introduction inlet 1418 to concentrate the sample and improveanalysis accuracy. An ionizer 1422 provides ionization of the sampleusing, for example, a radioactive Ni⁶³ foil, or non-radioactive plasmaionizer, or other suitable ionization source within ionization region1424. A plasma ionizer has the advantage of enabling precise control ofthe energy imparted to the sample gas for ionization. Ideally, theionizer 1422 imparts only enough energy to ionize the sample gas,without producing nitric oxides (NOx's) and ozone. A fragmentationregion may also be included in the system 1400. NOx's and ozone areundesirable because they can form ion species that interfere with theionization of CWA agents. Because diffusion and mobility constantsgenerally depend on pressure and temperature, the DMS analyzer system1400 may include a temperature sensor 1426 and/or a pressure sensor 1428for regulating the temperature and/or pressure of the sample gas withinthe analyzer unit 1410 for more accurate analysis. The analyzer 1410 mayalso include a humidity sensor. The analyzer 1410 also includes ananalytical region 1440 with filter plates 1442 and detector plates 1444.A molecular sieve 1446 may be employed to trap spent analytes.

The controller 1446 provides control of filtering and detection whilealso providing an output of the detection results. The power supply 1448provides power to the filter plates 1442, solid-state flow generator1402, and any other component requiring electrical power. The controllerelectronics 1446 for Vcomp, Vrf, the ion heater pumping, the DMS ionmotion, and the pre-concentrator 1420 heater may be located with theanalyzer unit 1410. Also, the detector 1444 electronics, pressure 1426and temperature 1428 sensors, and the processing algorithm for a digitalprocessor may reside within analyzer 1410.

At atmospheric pressure, to realize the benefits of mobilitynonlinearity, the DMS analyzer system 1400 illustratively employs RFelectric fields of about 10⁶ V/m, and a Vrf of about 200 Vpeak at abouta 200×10⁻⁶ μm gap. However, any suitable RF electric field parametersmay be employed. The power supply 1448 may be remotely located relativeto the analyzer unit 1410 to generate RF voltage for the filter plates1442. At less than atmospheric pressure, the RF electric field may bereduced as described above to further reduce the power consumption andsize of the DMS analyzer system 1400.

The DMS analyzer system 1400 may also interface with a personal computer(PC) or controller 1446 to utilized signal-processing algorithms thatconvert analyzer 1410 outputs into detection, identification, and/ormeasurement of analytes and concentration levels. The controller 1446 oran interfacing PC may also facilitate control and power management forthe DMS analyzer system 1400. The supporting electronics for the DMSanalyzer system 1400 may be implemented, for example, on an ASIC, adiscrete printed circuit board (PCB), or System on a Chip (SOC).

In operation, the solid-state flow generator or electromechanicaltransport pump 1402 draws samples into the DMS analyzer system 1400 atthe inlet 1414 and past a CWA-selective chemical membrane concentrator1420 having an integrated heater. The CWA-selective chemical membranepre-concentrator 1420 may also serve as a hydrophobic barrier betweenthe analytical region 1440 of the analyzer system 1400 and the sampleintroduction region 1450. The membrane of the pre-concentrator 1420,illustratively, allows CWA agents to pass, but reduces the transmissionof other interferants and acts as a barrier for moisture.

The pre-concentrator 1420 may use selective membrane polymers tosuppress or block common interferences (e.g., burning cardboard) whileallowing CWA agents or CWA simulants to pass through its membrane.Although many selective membrane materials are available, poly-dimethylsiloxane (PDMS) may be a preferred membrane/concentrator/filter toreject water vapor and collect CWA analytes. At high concentrationlevels, water vapor molecules may cluster to the analytes, altering theanalytes' mobilities. Membrane materials such as hydrophobic PDMS tendto reduce the vapor to acceptable levels while absorbing and releasinganalyte atoms. The thin membrane of the pre-concentrator 1420 may alsobe heated periodically to deliver concentrated analytes to theionization region 1424 and analytical region 1440.

Except for diffusion of analytes through themembrane/filter/pre-concentrator 1420, the analytical region 1440 isgenerally sealed to the outside atmosphere. Thus, the analyzer system1400 may employ elements for equalizing the pressure inside analyticalregion 1440 with the atmospheric pressure outside the analyzer system1400 or maintain pressure in the analytical region 1440 at less thanatmospheric pressure for improved ion intensity peak resolution. Oncethe sample gas molecules are ionized, the ions are driven longitudinallyin the direction indicated by the arrow 1452 through the ion filterplates 1442 by static or traveling electrostatic fields, as opposed tobeing driven by the carrier gas. The filter plates 1442 apply transverseradio frequency (RF) field voltages and dc excitation electriccompensation fields to the ions moving through analytical region 1440 toseparate the species within a sample.

With water vapor removed, interferants (e.g., hydrocarbons and others)typically comprise roughly 0.10% of the incoming air volume by weight.Depending on the collection efficiency of the pre-concentrator 1420, themolecular sieve 1446 may be sized to support about 6, 9, 12 or moremonths of substantially continuous or continuous operation beforesaturating. The molecular sieve 1446 may also be configured to allowmovement of air in a circulatory fashion through the ion filterelectrodes 1442 and back to the ionization region 1424.

The DMS analyzer system 1400 may be used for detecting lowconcentrations (e.g., parts per trillion (ppt)) of CWAs, such as,without limitation, nerve and blister agents. In one illustrativeembodiment, the DMS analyzer system 1400 includes a high-sensitivity,low-power, sample gas analyzer 1404 that builds on MEMS technology, butfurther miniaturizes the DMS analyzer system 1400 to achieveparts-per-trillion sensitivity, about 0.25 W overall power consumption(i.e., 1 Joule measurement every 4 seconds), and a size of about 2-cm³or less.

Because of the smaller analytical region 1440 and the resulting lowerflow rate requirements, a low-power (e.g., mW) solid-state gas transportpump 1402, using ionic displacement, may be employed to draw an airsample into the DMS analyzer system 1400 and onto the CWA-selectivechemical membrane pre-concentrator 1420. Compact DMS analyzer systemsaccording to the invention have shown very high sensitivities to CWAsimulants. By way of example, a compact DMS analyzer system according tothe invention has been shown to detect methyl salycilate atparts-per-trillion (ppt) levels. The DMS analyzer system 1400 has theability to resolve CWA simulants from interferants that cannot beresolved by current field-deployed detection technologies.

FIG. 42 is a graph depicting a DMS spectra showing resolution ofdimethylmethylphosphonate (DMMP) from aqueous firefighting foam (AFFF)as measured in a DMS analyzer system 1400. AFFF is one interferant thathas proved extremely challenging for conventional IMS systems to resolveCWAs or other simulants. The AFFF ion intensity peak tends to overlapwith the agent peak during sample detection in DMS or IMS systems.

FIG. 42 is a graph of multiple plots showing experimental results for aseries of CWA simulants selectively mixed with 1% headspace of AFFF. Thetop plot 1460 of FIG. 42 shows RIP for a DMS analyzer system 1400 withbackground air but no sample present with the sensor at atmosphericpressure. In the next plot 1462, the AFFF interferant is added. Thisresults only in a slight shift to the left (more negative compensationvoltage) of the RIP ion intensity peak. Then, in plot 1464, the CWAsimulant DMMP is introduced into the spectrometer and the typicalmonomer and dimmer peaks appear together with a corresponding reductionin the RIP peak ion intensity. When 1% AFFF is added according to plot1468, the DMMP peaks are not effected and only a slight leftward shiftof the RIP is observed. The same experiment was repeated with DIMP inplots 1468 and 1470, and the effect of AFFF was negligible. In plot1472, MS is introduced, and according to monitored negative ion peaks,gives similar data illustrating the lack of interference with AFFF. Theconclusion is that 1% AFFF has virtually no effect. Thus, FIG. 42illustrates the ability of the DMS analysis system 1400 to resolve CWAsimulants from interferants.

In one illustrative embodiment, the compact hand-held DMS analyzersystem 1400 is achieved by combining the following designcharacteristics: (a) using the analyzer/filter/detector 1410 withimproved sensitivity and size reduction; (b) using the solid-state flowgenerator or electromechanical pump as a gas transport pump 1402 tosample and move analytes; (c) using the CWA-selective chemical membranepre-concentrator 1420 with integrated heater (in some configurationsprovided by using a solid-state generator or electromechanical pump totransfer heat from other analyzer system components to thepre-concentrator 1420) to remove water vapor and to concentrate; and/or(d) using electric field propulsion of the ions 1454 through theanalytical region 1440 of analyzer 1410.

According to various illustrative embodiments, the invention improvesthe resolution of species identification over conventional systems,while decreasing size and power to achieve parts-per-trillionsensitivity, a less than about 0.25 mW overall power dissipation, and asize of about a 2-cm³ or less in an entire system not including a powersource or display, but including an RF field generator. According tosome embodiments, an analyzer system of the invention has a total powerdissipation of less than about 15 W, about 10 W, about 5 W, about 2.5 W,about 1 W, about 500 mW, about 100 mW, about 50 mW, about 10 mW, about 5mW, about 2.5 mW, about 1 mW, and/or about 0.5 mW. According to furtherembodiments, an analyzer system according to the invention, optionallyincluding a display (e.g., indicator lights and/or an alphanumericdisplay) and a power source (e.g., a rechargeable battery) compartment,along with an RF field generator, may have a total package outerdimension of less than about 0.016 m³, 0.0125 m³, 0.01 m³, 0.0056 m³,0.005 m³, 0.002 m³, 0.00175 m³, 0.0015 m³, 0.00125 m³, 0.001 m³, 750cm³, 625 cm³, 500 cm³, 250 cm³, 100 cm³, 50 cm³, 25 cm³, 10 cm³, 5 cm³,2.5 cm³, with the package being made, for example, from a high impactplastic, a carbon fiber, or a metal. According to further embodiments,an analyzer system, for example, according to the invention, includingan RF generator, and optionally including a display, keypad, and powersource compartment, may have a total package weight of about 5 lbs, 3lbs, 1.75 lbs, 1 lbs, or 0.5 lbs.

Table 1 provides a comparison of drift tube (e.g., the constrainedchannel) dimensions, fundamental carrier gas velocities, and ionvelocities for a various illustrative embodiments of a DMS analyzersystem 1400 depending on the flow rate (Q) available to the analysisunit. Designs 1-4 provide flow rates of varying orders of magnituderanging from about 0.03 l/m to about 3.0 l/m. Table 1 illustrates thatas the flow rate is decreased through the DMS analyzer system 1400, thefilter plate dimensions and power requirements are reduced. Table 1 isapplicable to a DMS analyzer system 1400 using either a sample gas orlongitudinal field-induced ion motion. The time to remove an unwantedanalyte is preferably less than about the time for the carrier to flowthrough the filter region (tratio). Also, for a particular target agent,the lateral diffusion as the ion flows through the analyzer 1410 ispreferably less than about half the plate spacing (difratio). Based onthis criteria, the plate dimensions may be reduced to about 3×1 mm² orsmaller, while the ideal flow power may be reduced to less than about0.1 mW. Thus, even for design 4, the number of analyte ions striking thedetectors is sufficient to satisfy a parts-per-trillion detectionrequirement.

TABLE 1 Illustrative DMS Analyzer System Design Specifications andCharacteristics Design 1 Design 2 Design 3 Q = 3 l/m Q = 0.3 l/m Q = 0.3l/m Design 4 Description Units Symbol Baseline Base dimen scaled Q =0.03 l/m plate dimensions *length m L 0.025 0.025 0.005 0.001 *width m b0.002 0.002 0.001 0.0004 *air gap m h 0.0005 0.0005 0.0005 0.0002*volume flow rate l/min Qf 3 0.3 0.3 0.03 Flow velocity m/s Vf 50 5 106.25 pressure drop Pa dPf 1080 108 43.2 33.75 flow power W Powf 0.0540.00054 2.16E−04 1.69E·05 RF excitation V Vrf 650 650 650 260 designratios Time to remove unwanted analyte divided by carrier time s tratio0.0128 0.0013 0.0128 0.0160 wanted ions-lateral diffusion divided byhalf gap s difratio 0.200 0.632 0.200 0.283 ions to count per cycle —Nout 1.22E+07 1.22E+06 1.22E+06 1.22E+05

For sample/carrier gases, there does not appear to be anelectromechanical pump that operates at the preferred flowcharacteristics with an efficiency better than about 0.5%. With a 0.5%efficiency, an ideal flow loss of about 0.05 mW results in an actualpower consumption of about 10 mW, about a factor of 100 greater than inthe above discussed illustrative embodiment of the invention.

The DMS system 1400 may simultaneously detect both positive and negativeion intensity peaks which further improves detection selectivity. Thecombination of the positive and negative ion channel information, theshift in spectral peak as a function of applied field strength orvoltage, and the display is this information in a three-dimensionalmanner provide a novel mechanism for chemical identification.

FIG. 43 is a three-dimensional dispersion plot 1750 of the detection ofpositive ions of agent GA over a range of field voltages and fieldcompensation voltages with varying intensity represented in varyingcolor according previously described illustrative embodiments of theinvention. The plot 1750 illustrates the enhanced identification(selectivity) of a compound using a three-dimensional dispersion plotby, for example, a DMS system 1400. In comparison, FIG. 25 is athree-dimensional dispersion plot of negative ions of GA over a range ofRF voltage versus compensation voltage with varying intensityrepresented in varying color that illustrates the enhancedidentification (selectivity) of a compound using a three-dimensionaldispersion plot by, for example, DMS system 1400. Both measurements wereperformed with a concentration of GA at 0.14 ng/l, a Ni⁶³ source, 50%RH, 3 scan averaging, and 350 cc/min carrier gas flow. The differencesbetween the three-dimensional plots 814 of FIGS. 25 and 1750 of FIG. 50illustrate that performing both positive and negative ion mode detectionprovides enhanced signature identification of ion species.

In certain illustrative embodiments, the compact DMS system 1400 of FIG.41 and various other figures may employ features and/or be incorporatedinto systems described in further detail in U.S. Pat. Nos. 6,495,823 and6,512,224, the entire contents of both of which are incorporated hereinby reference.

FIGS. 44-53 are conceptual block diagrams of chemical and/or biologicalagent detection systems using various configurations of a mobilitydetection analyzer system such as those depicted and described herein, arecirculation system, and other components according to illustrativeembodiments of the invention. More particularly, FIG. 44 is a conceptualblock diagram of a CWA and/or biological agent detection system 1476according to an illustrative embodiment of the invention. The system1476 employs a mobility detection system 1478, molecular sieve 1480,pump 1482 with optional vent 1484, optional second molecular sieve 1486,circulating channel 1488, sample inlet 1490, exhaust 1492, membrane1494, and orifice 1496. The system 1476 may also employ filtered air orgas 1498 to circulate or transport a sample through the system 1476. Themobility analyzer system 1478 may be a compact DMS analyzer system 1400of FIG. 48, DMS system 10 of FIG. 5, an IMS, a TOF-IMS, a GC-IMS, an MSor the like. The system 1476, like all of the previously describedillustrative systems, may employ one or more dopants such as, methylenebromide (CH₂Br₂), methylene chloride (CH₂Cl₂), chloroform (CHCl₃), water(H₂O), methanol (CH₃OH), and/or isopropanol, introduced, mixed and/orflowed with the sample to enhance analysis.

In operation, the system 1476 receives a sample S at inlet 1490 andpasses it through the membrane 1494 into the circulation channel 1498.The membrane 1494 may filter out unwanted interferants, if desired, inthe same or similar manner as the pre-concentrator 1420 of FIG. 48. Theorifice 1496 may, in a fixed, controlled, or adjustable manner, regulatethe gas and/or sample flow into the analyzer system 1478 and therebyregulate or control the pressure within the analyzer system 1478. Thus,the analyzer system 1478 may operate at atmospheric pressure, belowatmospheric pressure, or above atmospheric pressure. The pump 1482maintains gas flow in the analyzer system 1478 and pressure controleither independently or in coordination with the orifice 1496. Thus, inone example, the pump 1482 draws sample flow through the orifice 1496into the analyzer system 1478 to enable detection and identification ofselected ion species. The analyzer system 1478 may be a DMS system 1400that tunably detects certain ion species by adjusting its field/flowchannel conditions, such as, its Vrf and Vcomp, parameters and in someconfigurations, controlling the pump 1484 and/or the orifice 1496 tocontrol pressure within the system 1400.

Once detection and identification are performed, the molecular sieve1480 may trap spent analytes from the analyzer system 1478. Again, thepump 1484, whether electromechanical or solid-state, propels the gas,optionally through a second molecular sieve 1486, through thecirculating channel 1488. The sample gas is then expelled through themembrane 1494 and the outlet 1492 or mixed and re-circulated with moresample S back into the orifice 1496.

FIG. 45 is a conceptual block diagram of a CWA and/or biological agentdetection system 1500, configured for reduced pressure analysis,according to an illustrative embodiment of the invention. The system1500 is similar to the system 1476 except that an additional sample flowchannel 1502 is employed instead of a membrane. The system 1500 includessample S inlet 1504, orifice 1506, ionization region 1508, deflectorplate 1510, attractor plate 1512, channel 1502 pump 1514, second channel1516, analyzer system 1518, molecular sieve 1520, pump 1522, andoptional second molecular sieve 1524.

In operation, the system 1500 draws sample S through the sample inlet1504 and through the orifice 1506. The orifice 1506 may be controlled,fixed, or adjustable to regulate sample gas flow and/or pressure in thechannel 1502. The pump 1514 may also be used in coordination with theorifice 1506 to regulate gas flow and/or pressure within the channel1502. The deflector plate 1510 may force, push, or selectively separateions into the channel 1516 through the opening 1526 while the attractor1512 may attract ions from the channel 1502 into the channel 1516. Apressure drop across the opening 1526 may be adjusted so that onlysample ions enter the channel 1516 while sample neutrals are preventedfrom entering. The sample ions may be directly introduced into theanalyzer system 1518 or the ions may be neutralized and then re-ionizedin the analyzer system 1518. The analyzer system 1518 may be a DMSsystem, IMS system, or the like. The analyzer system 1518 may includemultiple DMS, IMS, or other like systems or a combination of suchsystems to perform sample detection and identification. For example,system 748 of FIG. 21 or system 754 of FIG. 22 may be employed to applyconventional DMS detection in combination with fragmentation to enhancesample analysis.

The channel 1516 pump 1524 may then draw the sample S from the analyzersystem 1518 through the molecular sieve 1520 and then propel the sampleS, optionally through the second molecular sieve 1524. The molecularsieves 1520 and 1524 will capture most of the spent sample S analytes.Any remaining sample S is mixed with new sample S gas and returned tothe analyzer system 1518 via the channel 1516. The outlet 1528 expelssample S gas from the channel 1502.

FIG. 46 is a conceptual block diagram of a cylindrical or coaxial CWAand/or biological agent detection system 1530 according to anillustrative embodiment of the invention. The system 1530 includes asample S inlet 1532, constrictor 1534, inner channel 1536, opening 1538,clean transport gas inlet 1540, outer channel 1542, analyzer system1544, channel 1542 outlet 1546, and channel 1536 outlet 1548.

In operation, the system 1530 draws the sample S into the channel 1536through the constrictor or orifice 1534. The constrictor 1534 may beadjustable, controllable or fixed to enable a pressure reduction below 1atm, for example to 0.5, 0.65, or 0.85 atm, in the channel 1536. Theclean transport gas inlet 1540 receives clean transport gas into thechannel 1542. The channel 1542 may operate at pressures below 1 atm. Thesample S may be drawn or attracted into the channel 1542 through theopening 1538 by a pressure differential with the channel 1536, an ionattractor in channel 1542, gas flow into channel 1542, or other liketechnique. The analyzer system 1544 then detects and identifies the ionspecies of the sample S and expels the sample S through the outlet 1546.The sample neutrals in the channel 1536 may be expelled through theoutlet 1548.

FIG. 47 is a DMS system 1550 including an orifice 1552 at the system1550 inlet to control pressure within the system 1550 in coordinationwith a pump 1554. The system also includes the molecular sieve 1556, ionsource 1558, filter 1560, and detector 1562. In operation, the pump 1554has sufficient power to draw a sample S through the orifice 1552 to thenenable detection of the sample at a reduced pressure.

FIG. 48 is a DMS system 1564 including an orifice 1566, ionizationsource 1568, filter 1570, detector 1572, molecular sieve 1574, pump1576, a second molecular sieve 1578, a membrane 1580, an inlet 1582, andoutlets 1584 and 1586. Because the membrane 1580 is positioned upstreamof the orifice 1566 and the sample flow is in direction 1588, themembrane 1580 operates at atmospheric pressure while the ionizationsource 1568, filter 1570, and detector 1572 operate below atmosphericpressure due to a pressure drop across the orifice 1566. It may beadvantageous to operate the membrane 1580 at atmospheric pressure toprolong its useful life.

FIG. 49 is a DMS system 1590 including an orifice 1592, ionizationsource 1594, filter 1596, detector 1598, molecular sieve 1600, pump1602, a second molecular sieve 1604, a membrane 1606, an inlet 1608, andoutlets 1610 and 1612. Because the membrane 1606 is positioneddownstream of the orifice 1592 and the sample flow is in the direction1614, the membrane 1606 operates below atmospheric pressure along withthe ionization source 1594, filter 1596, and detector 1598 due to apressure drop across the orifice 1592. It may be advantageous to operatethe membrane 1606 below atmospheric pressure.

FIG. 50 is a DMS system 1616 including an orifice 1618, ionizationsource 1620, filter 1622, detector 1624, molecular sieve 1626, pump1628, a second molecular sieve 1630, a membrane 1632, an inlet 1634, andoutlets 1636 and 1638. Because the membrane 1632 and the ionizationsource 1620 are positioned upstream of the orifice 1618 and the sampleflow is in direction 1640, the membrane 1632 and the ionization source1620 operate at atmospheric pressure while the filter 1622 and detector1624 operate below atmospheric pressure due to a pressure drop acrossthe orifice 1618. It may be advantageous to operate the membrane 1632and ionization source 1620 at atmospheric pressure.

FIG. 51 is a DMS system 1642 including a first channel 1644 and a secondchannel 1646 operating at atmospheric pressure. The first channel 1644includes an ionization source 1648, deflector electrode 1650, pump 1652,inlet 1666, and outlet 1668. The second channel 1646 includes a filter1654, detector 1656, molecular sieve 1658, pump 1660, and molecularsieve 1662. An opening 1664 provides fluid communication between thechannels 1644 and 1646.

In operation, the system 1642 receives a sample S at the inlet 1666 intothe channel 1644. The ionization source 1648 ionizes the sample S. Theionized portions of the sample S, e.g., the positive ions, are deflectedthrough the opening 1664 into the channel 1646 by the deflector 1650having a positive charge. When the deflector 1650 is negatively charged,the deflector 1650 may deflect negative ions of sample S through theopening 1664 into the channel 1646. The neutrals and non-deflected ionsof sample S are then drawn by the pump 1652 to the outlet 1668 andexpelled from the system 1642 while the ions in the channel 1646 arefiltered by the filter 1654 and detected by the detector 1656. The pump1660 creates circulation flow in the direction 1670 within the channel1646 to draw the sample S through the molecular sieve 1658 whichcollects spent analytes and then through a second molecular sieve 1662.

FIG. 52 is a DMS system 1672 including a first channel 1674 and a secondchannel 1676 operating below atmospheric pressure without a membrane.The first channel 1674 includes an ionization source 1678, deflectorelectrode 1680, pump 1682, inlet 1684, outlet 1686, and orifice 1700.The second channel 1676 includes a filter 1688, detector 1690, molecularsieve 1692, pump 1694, molecular sieve 1696, and orifice 1702. Anopening 1698 provides fluid communication between the channels 1674 and1676.

In operation, the system 1672 receives a sample S at the inlet 1684 intothe channel 1674 and through the orifice 1700. The orifice 1700 providesa pressure drop within the channel 1674 caused by the gas and/or airflow generated by the pump 1682. The ionization source 1678 ionizes thesample S. The ionized portions of the sample S, e.g., the positive ions,are deflected through the opening 1698 into the channel 1676 by thedeflector 1680 having a positive charge. When the deflector 1680 isnegatively charged, the deflector 1680 may deflect negative ions ofsample S through the opening 1698 into the channel 1676. The neutralsand non-deflected ions of sample S are then drawn by the pump 1682 tothe outlet 1686 and expelled from the system 1672 while the ions in thechannel 1676 are filtered by the filter 1688 and detected by thedetector 1690. The pump 1694 creates circulation flow in the direction1704 within the channel 1676 to draw the sample S through the molecularsieve 1692 which collects spent analytes and then through a secondmolecular sieve 1696.

FIG. 53 is a DMS system 1706 including a first channel 1708, a secondchannel 1710, and a third channel 1712 with the second channel 1710 andthird channel 1712 capable of operating at or below atmospheric pressureusing a membrane 1714. The first channel 1708 includes an inlet 1716 andan outlet 1718. The second channel 1710 includes an ionization source1718, optional ionization source 1720, deflector electrode 1722, filter1724, and detector 1726. The third channel 1712 includes an attractorelectrode 1728, filter 1730, and detector 1732. The combined circulationchannel 1734 includes the chemical filter 1736, pump 1738, and optionalchemical filter 1740. An opening 1742 provides fluid communicationbetween the channels 1710 and 1712.

In operation, the system 1706 receives a sample S at the inlet 1716 intothe channel 1708. The sample S may be introduced from a GS column. Themembrane 1714 may filter a portion of the sample S and provide apressure barrier to enable a pressure below atmospheric pressure in thechannels 1710 and 1712. The channels 1710 and 1712, along with thecombined circulation channel 1734, circulate filtered and clean carriergas. The ionization source 1718 ionizes the sample S within this cleancarrier gas. Optionally, a second ionization source 1720 may be employedin the channel 1710 to enhance the ability of the deflector 1722 andattractor 1728 to transfer selected ions from the channel 1710 to thechannel 1712. For example, the ionized portions of the sample S, e.g.,the positive ions, are deflected through the opening 1742 into thechannel 1712 by the deflector 1722 when the deflector 1722 is positivelycharged. When the deflector 1722 is negatively charged, the deflector1722 may deflect negative ions of sample S through the opening 1728 intothe channel 1712.

The neutrals and non-deflected ions of sample S are then drawn by thepump 1738 through the channel 1710, filter 1724 and detector 1726 whilethe selected ions are drawn through the channel 1712, filter 1730, anddetector 1732. The pump 1738 creates circulation flow in the direction1744 within the channels 1710, 1712, and 1734 to draw the carrier gasfrom the channels 1710 and 1712 into the channel 1734 and through thechemical filter 1736 and, optionally, the second chemical filter 1740.The chemical filters 1736 and 1740 remove unwanted contaminants from thecarrier gas. A make up gas may also optionally be introduced into thechannel 1734 from an outside system.

The deflector 1722 and the attractor 1728 may be activated in acontrolled manner to transport ions from the channel 1710 to the channel1712. In the channel 1710, the non-deflected ions are filtered by filter1724 and detected by detector 1726 while, in the channel 1712, thedeflected and attracted ions are filtered by the filter 1730 anddetector 1732. The resulting detected measurements from the channels1710 and 1712 can then be compared, added, or subtracted from each otherto enhance the identification of ion species. The controlled ionizationof the sample S which is performed in a clean carrier gas, the detectionin the channel 1712 of monomer or de-clustered ions, and the detectionof clustered ions in the channel 1710 provide enhanced compound and ionspecies identification.

Other illustrative embodiments include systems, methods and devices forimproving sample analysis, generally, and detection sensitivity,specifically, by performing sample ion species pre-separation and/orsample amplification. Such illustrative embodiments are discussed below.

Pre-separation of certain ion species of a sample reduces, and in somecases, eliminates the problem of competitive ionization within ion basedmobility detection analyzers. At any atmospheric pressure or conditionswhere ion and/or neutral interactions have an effect on ion formation,atmospheric pressure chemical ionization (APCI) may occur. In suchinstances, compounds with the highest proton affinity (PA) and/orhighest electron affinity (EA) preferentially capture or take up thecharge from an ionization source. If there is a limited amount of chargeavailable, for example, in a compact DMS system with limited powerresources, the amount of available charge may not be sufficient tocharge or ionize all of the molecules in a sample matrix. Thus, if onlysome of the molecules in a sample matrix are ionized, only that limitedamount of molecules may be detected, resulting in erroneous analysis ofa chemical matrix. Furthermore, certain compounds may not be ionized dueto competitive ionization, resulting in no detection of these compounds.The invention includes embodiments that eliminate or mitigate theeffects of competitive ionization by separating ion species beforesample analysis or detection to prevent one ion species from consumingthe charge intended to be used to ionize another ion species.

One technique for reducing the effect of competitive ionization is touse a gas chromatograph (GC) to pre-separate a sample matrix. A GCcolumn may be used to separate multiple compounds, which may then bedetected individually by a mobility-based analyzer, such as a DMS. Evena compound with a relatively low proton and/or electron affinity may besubsequently ionized and detected. A GC, however, is generally morecomplex, expensive, and often adds significant analysis time to providesufficient compound separation. Typical analysis times are longer thanone minute for sufficient compound separation. Thus, the inventionincludes systems, methods and devices for pre-separating a sample in afast, efficient, and robust manner. According to other aspects, theinvention provides such sample pre-separation in a compact package.Thus, the invention includes systems, methods and devices forpre-separating a sample in a fast, efficient, and robust manner.According to other aspects, the invention provides such samplepre-separation in a compact package.

Where further sample characterization is desired, neutrals, i.e.,molecules of a sample that are not ionized, may be mixed with a newsupply of charge, e.g., reactant ions or a plasma field, to enablefurther APCI reactions to occur. The newly created ions may then beremoved for analysis or simply discarded. This process may be repeateduntil a desired compound type is ionized and detected using an analyzer.

In one embodiment of the invention, sample pre-fractionation is achievedby direct ionization of a sample matrix, competitive ionization bycompounds of a certain type in the sample matrix, and then removal ofthe ionized compounds. The ionization source may be, for example, an UVsource, laser, corona discharge, plasma source, soft X-ray source, or asource of reactant ions. Repeated interrogation of chemical compounds ina sample based on relative proton and electron affinities, usingcompetitive ionization and the reaction of residual and/or un-reactedneutrals provides a comprehensive measure of the chemical composition ofa sample without the need for traditional GC techniques.

The process of competitive ionization and the removal of product ionsmay be repeated, enabling incremental and selective isolation of productions and neutrals. While chemical ionization involves the injection offresh charge using reactant ions, non-chemical energy sources such as alaser or plasma or corona generator may ionize molecules of a sample.

In addition to being used for analysis, the invention may be used forselectively cleaning and/or conditioning samples, e.g., for removingselected molecules from a sample stream. For example, certainsemiconductor industry or other process control applications requireultra pure or clean gasses. In these processes, water molecules areconsidered a contaminant in a gas stream of Nitrogen or Argon. Incertain embodiments of the invention, water within a gas sample may bepreferentially ionized and then removed from the gas stream whilepurified Argon or Nitrogen are then used in a low pressure chemicalvapor deposition or for another semiconductor application.

FIG. 54A is a conceptual diagram showing an example of a pre-separationprocess 1750 of a sample matrix 1752 including two types of compoundmolecules 1756 and 1758 according to an illustrative embodiment of theinvention. The process 1750 begins by mixing reactant ions 1754 with asample matrix of the two types of compound molecules 1756 and 1758 witha source of reactant ions 1754 to form a reactant ion and sample matrixmixture 1760.

This mixing may involve injecting (e.g., via an injection pulse) thesample matrix 1752 into a re-circulating or circular flow of gas wherethe mixing of reactant ions 1754 with neutral molecules 1756 and 1758can be controlled. Also, the injection of reactant ions 1754 andsubsequent extraction of product ions, e.g., product ions 1762, can beenabled using orifices in an ionization region, chamber, or gas flowpath. Alternatively, a linear scheme may be employed where reactant ions1754 are continuously introduced. In this scheme product ions, e.g.,product ions 1762, are removed at discrete or variable distances fromthe injection point of sample matrix 1752 or the product ion formationpoint. In either case, the effluent flow (e.g., the flow of gas) may beused to control or adjust the residence or contact times betweenreactant ions 1754 and neutral molecules 1756 and 1758 to control theformation of product ions such as product ions 1762 or 1764.

Because the compound molecules 1756 are preferentially ionized by thereactant ions 1754, the mixture 1760 includes un-ionized compoundmolecules 1756 and product ions 1762. The product ions 1762 may beseparated from the compound 1758 using chemical, electrical, magnetic,and/or a mechanical separation technique to remove the product ions1762. The ionized molecules or product ions 1762 may then be analyzedand characterized, for example, using a DMS, IMS, MS, or any suitableanalyzer system or may be discarded.

Because the first type of compound molecules 1756 are preferentiallyionized to form ionized molecules or product ions 1762, the second typeof compound molecules 1758 predominately are not ionized and retain aneutral charge. However, the source of reactant ions 1754 may bere-introduced to and mixed with the remaining neutral molecules 1758 toform ionized molecules or product ions 1764. These product ions 1764 maythen be separated and analyzed. The process 1750 may be repeated for anysample matrix with any number of compounds by repeatedly ionizing thesample matrix and removing the resulting product ions. Due tocompetitive ionization, the process incrementally removes differentcompounds with different ionization energies, enabling a comprehensiveanalysis of all compounds with a chemical sample.

FIG. 54B is a conceptual diagram showing the pre-separation process 1768of a sample matrix 1770 including two types of compound molecules 1772and 1774 using an ionization source 1778 and electric field 1776according to an illustrative embodiment of the invention. In this case,an ionization source 1778, such as a plasma corona, laser, UV source, orthe like, is used to ionize the sample matrix 1770. Due to competitiveionization, the molecules 1774 predominantly are ionized into productions 1780. These product ions 1780 are then exposed to the electricfield 1776 which substantially removes the product ions 1780 from theionized sample matrix 1782. The removed product ions 1780 may beanalyzed or discarded.

The remaining non-ionized neutral molecules 1772 may then be ionizedusing the same ionization source 1778 or another ionization source toform product ions 1784. The product ions 1784 may then be analyzed usinga DMS or discarded. The electric field 1776 may be generated by any oneof or combination of a deflector plate deflector array, attractor plate,attractor grid, and attractor array or various other electrodes.Alternatively, a magnetic field may be employed to remove selectedproduct ions.

FIG. 55 is a conceptual block diagram of a sample pre-separation system1786. The pre-separation system 1786 uses first and second ionizationregions 1788 and 1790 and first and second deflector regions 1792 and1794 to separate a sample matrix S. Sample matrix S includes at leasttwo compounds according to an illustrative embodiment of the invention.The sample pre-separation system 1786 includes an inlet 1796, gas flowchannel 1798, first ionization region 1788, first deflector region 1792,first deflector plate 1800, first attractor plates 1802, first exhaust1804, first optional analyzer 1806, pump 1808, second ionization region1790, second deflector region 1794, second deflector plate 1810, secondattractor plates 1812, second exhaust 1814, second optional analyzer1816, and the exhaust channel 1818.

In operation, the sample matrix S is drawn into gas the flow channel1798 through the inlet 1796 and then ionized in the first ionizationregion 1788. The sample S may be ionized using reactant ions or any ofthe non-reactant ion sources described previously. Due to the chemicalproperties of the molecules, the limited supply of charge leads tocompetitive ionization where predominantly certain types of compoundmolecules are ionized into product ions while other types of compoundmolecules predominantly remain neutral. The first deflector plate orelectrode 1800 and the first attractor plates or electrodes 1802generate an electric field that propels the product ions out of the gasflow channel 1798 and through first exhaust 1804. The first exhaust 1804may deliver the product ions to an analyzer for detection andidentification of the product ion species. Otherwise, the first exhaust1804 may simply discard the product ions into the surroundingenvironment or neutralize them.

The remaining neutral molecules continue to travel in the gas flowchannel 1798 and may pass through the first optional analyzer 1806. Theanalyzer 1806 may be a DMS system that ionizes the remaining neutralmolecules, performs a non-destructive detection and identification, andthen neutralizes the molecules before returning the neutrals to the gasflow channel 1798. The neutral molecules then continue to travel in thegas flow channel 1798 in the direction 1819 toward pump 1808 whichpropels the neutrals to the second ionization region 1790. In the secondionization region 1790, another type of compound molecule becomespredominantly ionized into product ions due to competitive ionizationwhile one or more other compound molecules remain neutral in charge.

In the second deflector region 1794, second deflector plate 1810 andsecond attractor plates 1812 generate an electric field that propels theproduct ions out of the gas flow channel 1798 and through the secondexhaust 1814. The second exhaust 1814 may deliver the product ions to ananalyzer for detection and identification of the product ion species.Otherwise, the second exhaust 1814 may simply discard the product ionsinto the surrounding environment.

Again, the remaining neutral molecules continue to travel in the gasflow channel 1798 and may pass through an optional analyzer 1816. Theanalyzer 1816 may be a DMS system that ionizes the remaining neutralmolecules, performs a detection and identification, and then neutralizesthe molecules before returning the neutrals to the gas flow channel1798. The neutral molecules may then continue to travel through theexhaust channel 1818 to yet further ionization regions and analyzers forfurther analysis or be discarded.

FIG. 56A is a conceptual diagram of a sample pre-separation process 1820according to a second illustrative embodiment of the invention. In thesample pre-separation process 1820, a sample matrix 1822 may bere-circulated multiple times to interact with an ionization source suchas reactant ions 1824. The sample pre-separation process 1820 may removedifferent compound product ions 1826 from the sample matrix 1822 in eachcirculation. The process 1820 begins with the mixing of the samplematrix 1822 in an interaction region with a source of reactant ions 1824to form an interaction region mixture 1828. Due to competitiveionization, the types of compounds within the sample matrix 1822 withrelatively higher proton and electron affinities tend to become ionized.Other types of compounds in the sample matrix 1822 with lower proton andelectron affinities tend to remain neutral.

The ionized molecules, or product ions 1826, are then removed from themixture 1828 using previously described techniques such as an electricor magnetic field. The remaining neutral molecules 1830 arere-circulated for further ionization. Prior to further ionization, theremaining neutral molecules 1830 may optionally be subjected tomobility-based analysis using, for example, a DMS system 1832. After theanalysis, the neutral molecules 1830 are then delivered to aninteraction region for further mixing with reactant ions 1824.

The resulting neutral molecules 1830 may be re-circulated multipletimes. Each time, the sample 1822 or remaining sample matrix 1830interacts with reactant ions 1824 enabling the incremental removal ofdifferent compound molecules from the sample 1822. The compound removedin each re-circulation tends to have a lower proton or electron affinitythan the compounds removed in a previous re-circulation. The remainingneutral molecules 1830 may also be delivered to an analyzer 1834 after asequence of iterations for detection and identification of a desired ionspecies.

FIG. 56B is a conceptual diagram of a sample pre-separation process 1836according to another illustrative embodiment of the invention. In thesample pre-separation process 1836, a sample matrix 1838 including atleast two types of compound molecules 1840 and 1842, are re-circulatedmultiple times to interact with an ionization source 1844 and anelectric field 1846. As a result, the sample pre-separation processsequentially removes different compound product ions. In this case, theionization source 1844, such as a plasma field, laser, UV source, orlike, is used to ionize the sample matrix 1838 to create an ionizedsample matrix 1850. Due to competitive ionization, molecules 1842 tendto be ionized into product ions 1848 in favor of molecules 1840. Theseproduct ions 1848 are then exposed to the electric field 1846 whichremoves the product ions 1848 from the ionized sample matrix 1850. Theproduct ions 1848 may be analyzed or discarded.

The remaining non-ionized neutral molecules 1840 may then be ionized byre-circulating the molecules 1840 to the same ionization source 1844 toform product ions 1852. The product ions 1852 may then be analyzed usinga DMS or discarded. The electric field 1846 may be generated by any oneof or combination of a deflector plate or electrode, deflector array,attractor plate or electrode, attractor grid, or attractor array.Alternatively, a magnetic field may be employed to remove selectedproduct ions. This process may be applied to a matrix with anundetermined number of compounds by repeatedly re-circulating the samplethrough the same ion source to thoroughly characterize and/or identifyall of the sample's constituents. The sample matrix may be introducedinto the pre-separator as a plug or as a continuous stream.

FIG. 57 is a conceptual block diagram of a sample pre-separation system1854 according to another illustrative embodiment of the invention. Thesample pre-separation system 1854 re-circulates a sample matrix Sthrough an ionization region 1856 multiple times. During each iteration,the sample pre-separation system 1854 removes a different compound fromthe sample matrix S. The compound removed on each iteration has a lowerproton affinity or electron affinity than the compound removed in theprior iterations. The sample pre-separation system 1854 includes inlet1858, inlet valve 1876, gas flow channel 1860, ionization region 1856,ion deflector/reflector region 1864, exhaust 1862, pump 1866, bleedvalve 1868, analyzer valve 1870, flow channel valve 1872, and anoptional analyzer 1874.

In operation, a sample matrix S is drawn into the gas flow channel 1860through the inlet 1858 and the inlet valve 1876. The sample matrix S isthen ionized in the ionization region 1856. The ionization region 1856may utilize an ionization source such as a reactant ion source, UVsource, laser, and the like to ionize the sample S. Due to competitiveionization, certain types of compound molecules predominantly areionized into product ions while other types of compound molecules remainneutral. The deflector/reflector region 1864 includes a deflector and/orattractor electrodes that generate an electric field to propel theproduct ions out of the gas flow channel 1860 and through exhaust 1862.The first exhaust 1862 may deliver the product ions to an analyzer fordetection and identification of the product ion species. Otherwise, thefirst exhaust 1862 may simply discard the product ions into thesurrounding environment.

The remaining neutral molecules continue to travel in the gas flowchannel 1860 through pump 1866. Pump 1866 propels the neutral moleculestoward the analyzer valve 1870. The analyzer valve 1870 may be opened atcertain times or in predetermined cycles to allow a portion of sample Sthrough the valve 1870 to an analyzer. This controlled valve openingenables an analyzer such as a DMS, IMS, or MS to analyze a desired ionspecies without interference from undesired ion species. The gas flowchannel 1860 may also include a bleed valve 1868 to enable makeup gas tobe added or excessive gas to be removed from the gas flow channel 1860.Until the analyzer valve 1870 is operated, the neutral sample Smolecules will continue to flow through flow channel valve 1872 and maypass through an optional analyzer 1874. The analyzer 1874 may be a DMSor like system that ionizes the remaining neutral molecules, performs anon-destructive detection and identification, and then neutralizes themolecules before returning the neutrals to the gas flow channel 1860.The neutral molecules then continue to travel in the direction 1875through the gas flow channel 1860 and eventually return to theionization region 1856. Another type of compound molecule becomesionized into product ions due to competitive ionization while one ormore other types of compounds molecules remain neutral in charge. Thisre-circulation process may be continued until an ion species is selectedfor analysis by operating the analyzer valve 1870.

FIG. 58A is a conceptual diagram of a sample pre-separation system 1878where pre-selected reactant ions are intermixed with a sample stream toenable the pre-separation of ions having a particular proton orelectronic affinity according to an illustrative embodiment of theinvention. The pre-separation system 1878 includes a selected reactantion type 1880, a sample stream 1882, a mixing unit 1884, a controllerunit 1886, product ions 1888, and neutral molecules 1890.

In operation, a selected reactant ion species type 1880 is introduced tothe mixer 1884 along with a sample stream 1882. The reactant ion speciescan be, for example, oxygen ions or acetone ions. The mixer 1884includes an interaction or mixer region that enables sample stream 1882molecules of a relatively higher proton or electron affinity to beionized into product ions 1888. Most molecules of a relatively lowerproton or electron affinity remain neutral molecules 1890.

The controller 1886 is capable of regulating whether a single type ormultiple types of reactant ions 1880 may be introduced into the mixer1884 and mixed with the sample stream 1882. The type of reactant ionspecies may be selected based on a particular property such as protonaffinity, mobility, electron affinity, and/or chemical activity. Byintroducing a certain type of reactant ion or ions 1880, the controller1886 can determine which compound molecules or cluster of molecules ofthe sample stream 1882 are ionized. Thus, the controller 1886 may moreprecisely target particular compounds of the sample stream 1882 forfurther analysis or removal from the sample stream 1882. The controller1886 may also regulate effluent and/or gas flow through the mixingand/or ionization region to control the contact time between reactantions and sample molecules and, thereby, control the amount of ionizationthat occurs. This technique also applies to other types of ionizationsources such a lasers, UV source, and plasma generators.

FIG. 58B is a conceptual diagram of a sample pre-separation system 1892where pre-selected reactant ions 1894, having been filtered andpre-selected, are then intermixed with a sample matrix 1896 to enablethe pre-separation of ions having a particular proton or electronicaffinity according to an illustrative embodiment of the invention. Thepre-separation system 1892 includes pre selected reactant ions 1894, asample matrix 1896, an ion mixing region 1898, a product ion separator1900, optional analyzer 1902, and an analyzer 1904.

In operation, pre-selected reactant ions 1894 of a particular speciesare introduced to the ion mixing region 1898 along with a sample matrix1896. The reactant ions 1894 may be filtered and pre-selected using aDMS, IMS, MS, or like system. The ion mixer region 1898 enables thesample matrix 1896 molecules having proton or electron affinities abovethe proton and electron affinities of the pre-selected ions 1894 to beionized into product ions 1906 while molecules of a relatively lowerproton or electron affinity remain neutral molecules 1908. As describedpreviously, various techniques may be utilized to remove the productions 1906. An optional analyzer 1902 may be employed to analyze theproduct ions 1906. The optional analyzer 1902 may also include an arrayof mobility-based analyzers. The analyzer 1904, which may be a DMS, IMS,MS, or like, may be employed to analyze the remaining neutral molecules1908.

For example, ionized molecules such as Acetone may be selectivelyintroduced as reactant ions and mixed with a sample matrix to removesubstantially all molecules with proton affinities higher than Acetone'sproton affinity (812 KJ/mol). By mixing a sample matrix with sufficientAcetone ions, charge will preferentially be transferred to molecules inthe sample matrix with higher proton affinities than Acetone. Theionized molecules or product ions may then be separated form the samplematrix leaving neutral molecules having proton affinities less thanAcetone's proton affinity. Thus, by using a particular reactant ionspecies to ionize a sample matrix, selected species of a sample matrixmay be removed or isolated in a more precise and controlled manner.

In certain embodiment of the invention, multiple types of ionizationsources or alternating ionization sources may be employed together or ina sequential flow arrangement. Different ionization sources may beemployed to selectively remove ion species having incrementally lowerproton or electron affinities. Thus, molecules with higher proton orelectron affinities will be removed first. For example, a sample mayfirst be exposed to a low ionization source such as a UV source, laser,or other photo-ionization source to remove ion species with highaffinities. Then, the sample may be exposed to a higher ionizationsource such as a radioactive Ni⁶³ ionization source to remove ionsspecies with relatively lower affinities. Additional ionization sourceswith pre-determined ionization energies may be employed to removeadditional ion species until a desired ion species remains for analysisusing a DMS, IMS, MS, and like mobility-based analyzer.

FIG. 59A is a conceptual diagram of a sample pre-separation system 1910including two flow channels wherein multiple ion separations are enabledby multiple ionization sources according to an illustrative embodimentof the invention. The sample pre-separation system 1910 includes aninlet 1916, gas flow channel 1912, inlet 1918, gas flow channel 1914, UVionization source 1920, first Ni⁶³ ionization source 1922, second Ni⁶³ionization source 1924, first opening 1926, second opening 1928, thirdopening 1930, outlet 1932, and outlet 1934.

In operation, a sample matrix S is introduced into gas flow channel 1912through inlet 1916. The UV ionization source 1920 then ionizes thesample S matrix at a relatively low energy. Due to competitiveionization, the compound molecules of sample S having the lowestionization energies and highest affinities, e.g., ionization energies atabout or below the UV ionization energy level, are ionized to formproduct ions. These product ions are then deflected from gas flowchannel 1912 and/or attracted into gas flow channel 1914 through thefirst opening 1926 by the electrode 1919. These low energy product ionsmay then be delivered by gas flow channel 1914 through outlet 1934 to ananalyzer or discarded. The inlet 1918 accepts gas flow into gas flowchannel 1914 to enable the flow of product ions delivered from gas flowchannel 1912.

For example, assume the sample matrix S includes nitric oxide species(NOx). In such a case, NO and NO₂ are formed by direct ionizationbecause these are the only NOx species with ionization energies belowthe ionization energy of the UV source. Tables 2 and 3 provide lists ofpositive and negative NOx ion species equations respectively. Also,Table 4 shows the ionization energy, proton affinity, and electronaffinity for selected NOx ion species.

TABLE 2 Positive NOx Ion Species Equations NO + hv → NO⁺ + e⁻ NO⁺ +H₂O + M → (H₂O)NO⁺ + M (H₂O)NO⁺ + H₂O + M → (H₂O)₂NO⁺ + M(H₂O)_(n−1)NO⁺ + H₂O + M → (H₂O)_(n)NO⁺ + M (H₂O)₃NO⁺ + H₂O → HNO₂ +(H₂O)₃H⁺

TABLE 3 Negative NOx Ion Species Equations NO₂ + hv → NO + O NO₂ + O + M→ NO₃ + M NO₂ + e⁻ → NO₂ ⁻ NO₂ ⁻ + NO₃ → NO₂ + NO₃ ⁻ NO₂ ⁻ + NO₂ → NO +NO₃ ⁻

TABLE 4 NOx Ionization Energy, Proton Affinity, and Electron AffinityProton Ionization Electron Affinity Energy Affinity PA EI (eV) EA (eV)(KJ/mol) NO 9.26 0.026 531.8 NO₂ 9.58 2.3 591 NO₃ 12.57 3.9 n/a

After ionization occurs with respect to the UV ionization source 1920,the non-ionized or neutral molecules remaining in the gas flow channel1912 proceed to the first Ni⁶³ ionization source 1922. Due to thecompetitive ionization process, the remaining molecules of the samplematrix S with the highest affinities are ionized to form product ions.These product ions are then deflected from the gas flow channel 1912and/or attracted into the gas flow channel 1914 through the secondopening 1928 by the electrode 1921. These product ions may then bedelivered by the gas flow channel 1914 through the outlet 1934 to ananalyzer or discarded.

Assuming the sample matrix S includes NOx species, the negative polarityNOx compounds with the highest electron affinity such as NO₂ are NO₃ areremoved as product ions. FIG. 60 shows the electron affinities for NO₂are NO₃ respectively.

After ionization occurs with respect to the first Ni⁶³ ionization source1922, the non-ionized or neutral molecules remaining in the gas flowchannel 1912 proceed to the second Ni⁶³ ionization source 1924. Due tothe competitive ionization process, the remaining molecules of thesample matrix S with the highest affinities are ionized to form productions. These product ions are then deflected from the gas flow channel1912 and/or attracted into the gas flow channel 1914 through the thirdopening 1930 by the electrode 1923. These product ions may then bedelivered by the gas flow channel 1914 through the outlet 1934 to ananalyzer or discarded. Any remaining neutral molecules may be deliveredthrough the outlet 1932 to an analyzer for analysis.

Because the ionization process is dynamic and time dependent, theresidence time for a sample matrix S within the proximity of anionization source may be adjusted to form particular types of productions. Thus, the interaction time between an ionization source and asample matrix S may also be controlled to selectively remove certainproduct ion species. For example, with regard to the NOx ion species,the NO₃ ⁻ ion species may be formed by direct photo-ionization using aUV ionization source according to the equations listed in Table 3.

FIG. 59B is a conceptual diagram of a sample pre-separation system 1936having two flow channels wherein multiple ion separations are enabled bymultiple ionization sources including a plasma ionization source 1950according to an illustrative embodiment of the invention. The samplepre-separation system 1936 includes an inlet 1942, gas flow channel1938, inlet 1944, gas flow channel 1940, UV ionization source 1946, Ni⁶³ionization source 1948, plasma ionization source 1950, first opening1952, second opening 1954, third opening 1956, outlet 1958, and outlet1960.

In operation, a sample matrix S is introduced into gas flow channel 1938through inlet 1942. The UV ionization source 1946 then ionizes thesample S matrix at a relatively low energy. Due to competitiveionization, the compound molecules of sample S having the lowestionization energies and highest affinities, e.g., ionization energies atabout or below the UV ionization energy level, are ionized to formproduct ions. These product ions are then deflected from gas flowchannel 1938 and/or attracted into gas flow channel 1940 through thefirst opening 1952 by the electrode 1951. These low energy product ionsmay then be delivered by the gas flow channel 1940 through the outlet1960 to an analyzer or discarded. The inlet 1944 accepts gas flow intogas flow channel 1940 to enable the flow of product ions delivered fromthe gas flow channel 1938.

After ionization occurs with respect to the UV ionization source 1946,the non-ionized or neutral molecules remaining in the gas flow channel1938 proceed to the Ni⁶³ ionization source 1948. Due to the competitiveionization process, the remaining molecules of the sample matrix S withthe highest affinities are ionized to form product ions. These productions are then deflected from the gas flow channel 1938 and/or attractedinto gas flow channel 1940 through the second opening 1954 by theelectrode 1953. These product ions may then be delivered by the gas flowchannel 1940 through the outlet 1960 to an analyzer or discarded.

After ionization occurs with respect to the Ni⁶³ ionization source 1948,the non-ionized or neutral molecules remaining in the gas flow channel1938 proceed to the plasma ionization source 1950. Due to thecompetitive ionization process, the remaining molecules of the samplematrix S with the highest affinities are ionized to form product ions.These product ions are then deflected from gas flow channel 1938 and/orattracted into gas flow channel 1940 through the third opening 1956 bythe electrode 1955. These product ions may then be delivered by gas flowchannel 1940 through outlet 1960 to an analyzer or discarded. Anyremaining neutral molecules may be delivered through the outlet 1958 toan analyzer for analysis.

FIG. 60 is a graph 1962 of ionization energies required for various NOxion species to form either positive or negative ions by directphoto-ionization in air. The NOx species NO and NO₂ have relatively highaffinities as reflected by their DMS and mass spectra which are shown inFIGS. 61A, 61B, and 61C. FIG. 61A is a graph 1964 of relative intensityversus mass units showing the mass-spectra to positive NOx ion NO. FIG.61B is a graph 1966 of relative ion intensity versus mass units showingthe mass-spectra for positive NOx ion NO₂. FIG. 61C is a graph 1968 ofion intensity versus field compensation voltage showing the ionintensity peaks 1970 and 1972 for NO and NO₂ respectively.

FIG. 62 is a conceptual diagram of a cylindrical sample pre-separationsystem 1974 including an integrated cylindrical DMS 1976 or otheranalyzer according to an illustrative embodiment of the invention. Thesample pre-separation system 1974 includes an inlet 1978, gas flowchannel 1980, Ni⁶³ ionization source 1982, ionization region 1984,ionization region 1986, outlet 1988, and deflector outlets 1990, 1992,1994, 1996, 1998, and 2000. The system 1974 also includes a deflector2002, deflector 2004, voltage source 2006, voltage source 2008,insulator 2010, insulator 2012, and surrounding space 2014.

In operation, a sample matrix S is drawn into the gas flow channeland/or path 1980 and ionized by the Ni⁶³ ionization source. Due tocompetitive ionization, certain compounds within the sample matrix Swithin the highest affinities are ionized into product ions. Theseproduct ions are then deflected from the gas flow channel 1980 into thesurrounding space 2014 through deflector outlets 1990 and 1992. Thedeflector 2002 resides within the center of the coaxial gas flow channel1980 and holds an electric potential or voltage generated by the voltagesource 2006. The deflector 2002 potential is high enough to create anelectric field of sufficient strength to propel the product ions fromthe gas flow channel 1980 into the surrounding space 2014. Thesurrounding space 2014 may be an enclosed, substantially enclosed, orunenclosed path and/or channel. The surrounding space 2014 may be asecond gas flow channel surrounding the system 1974 that directs productions propelled from the gas flow channel 1980 to an analyzer or othersystem for further analysis.

The remaining neutral molecules of the sample matrix S then travel tothe ionization region 1984. Due to competitive ionization, certaincompound molecules within the remaining sample matrix S with the highestaffinities are ionized into a new group of product ions. These productions are then deflected from the gas flow channel 1980 into thesurrounding space 2014 through deflector outlets 1994 and 1996. Thedeflector 2002 potential is high enough to create an electric field ofsufficient strength to propel the product ions from the gas flow channel1980 into the surrounding space 2014.

The remaining neutral molecules of the sample matrix S then travel tothe ionization region 1986. Due to competitive ionization, certaincompound molecules within the remaining sample matrix S with the highestaffinities are ionized into a third group of product ions. These productions are then deflected from the gas flow channel 1980 into thesurrounding space 2014 through deflector outlets 1998 and 2000. Thedeflector 2004 resides within the center of the coaxial gas flow channel1980 and holds an electric potential or voltage generated by the voltagesource 2008. The deflector 2004 potential is high enough to create anelectric field of sufficient strength to propel the product ions fromthe gas flow channel 1980 into the surrounding space 2014. An insulator2010 provides electrical separation and enables an electrical potentialdifference between deflector 2002 and deflector 2004.

The remaining molecules of the sample matrix S, which preferably includethe compound of interest for detection, are then delivered to thecoaxial DMS system 1976 for analysis. The insulator 2012 provideselectrical separation between the deflector 2004 and the DMS ion filterelectrode 2016. The ionization regions 1984 and 1986 may use any one ofthe previously described ionization sources to ionize the sample matrixS.

In certain illustrative embodiments, a variable and/or adjustableionization energy source may be employed by the forgoing pre-separationsystems. For example, a tunable laser may be used as an adjustableionization source. A sample may then be repeatedly exposed to the laserionization source while the energy level of the laser is changed foreach ionization. By adjusting the laser energy level and the resultingionization energy, different molecules of a sample are ionized andseparated from the sample matrix. The wavelength or frequency of a lasermay be adjusted to enable the selective removal of molecules from asample.

In certain illustrative embodiments, the sample matrix environmentalconditions may be altered at various stages during the ionization andseparation process. For example, the level of moisture may be set at onelevel during the ionization process and then adjusted to another levelduring the extraction or removal process. By altering the environmentalconditions such as the moisture level at different stages of theionization and separation process the extraction of particular ions froma sample may be improved.

In other illustrative embodiments, dopants may be intermixed with asample in the mixing region of a pre-separation system to improve and/orcontrol the charge transfer to sample molecules from reactant ions.Different dopants may be added to a sample at different times and/or atvarious stages of the ionization and separation process. The dopants maybe added before, during, or after selected analytes or product ions areremoved from a sample matrix. For example, an inkjet like printer headmay be loaded with various types of dopants. The head may deploy one ormore dopants using injection pulses at various times and/or stages of anionization and separation process.

FIG. 63 is a conceptual block diagram of a sample pre-separation system2018 capable of mixing dopants with a sample matrix S in a controlledmanner before or after reactant ions are added according to anillustrative embodiment of the invention. The sample pre-separationsystem 2018 includes the inlet 2020, gas flow channel 2022, dopantsources 2024, ionization region 2026, ion deflector/reflector 2028, andpumps 2030.

In operation, a sample matrix S is drawn through inlet 2020 into the gasflow channel 2022. The dopant sources 2024 may include various types ofdopants. Any one of the dopants or a combination of dopants may be addedto the sample matrix S in the gas flow channel 2002. Each dopant source2024 may include an injection mechanism to inject or pulse controlledamounts of dopant into the gas flow channel 2002. When the sample matrixS and dopant mixture enter the ionization region, certain types ofcompound molecules of the sample matrix S are ionized due to competitiveionization.

Upon leaving the ionization region 2026, the ionized molecules orproduct ion are deflected by the deflector/reflector 2028 through outlet2032 to either an analyzer or an exhaust. The pumps 2030 re-circulatethe remaining neutral molecules through the gas flow channel 2022. Thedopant sources 2024 may again inject dopants into the gas flow channel2022 to enable mixing of selected dopants with the remaining neutralmolecules of the sample matrix S. This process may be repeated while thesample matrix S is re-circulated through the pre-separation system 2018until a selected compound or group of compounds are extracted from thesample matrix S.

In one illustrative embodiment of the invention, a device and/or systemmay be employed that uses multiple flow paths to combine variouscombinations of ions to control the formation and delivery of aparticular type of reactant ion species to a pre-separation system. Bycontrolling the type of reactant ion species introduced into anionization and mixing region, the type of compound of a sample that isionized may be controlled. For example, logic circuits may arranged froman array of DMS, IMS, MS, and the like filters to control the flow andcombination of various ion species into a pre-separation system.

FIG. 64 is a conceptual diagram of an array of logic circuits 2034including an “or” flow circuit 2036 and an “and” flow circuit 2038 usedto form a desired reactant ion species according to an illustrativeembodiment of the invention. The “or” flow circuit includes the sampleinlet 2040, sample inlet 2042, carrier gas inlet 2044, flow channel2050, flow channel 2052, flow channel 2054, opening 2046, opening 2048,and outlet 2056. The “and” flow circuit includes the sample inlet 2058,sample inlet 2060, carrier gas inlet 2062, flow channel 2068, flowchannel 2070, flow channel 2072, opening 2064, opening 2066, and outlet2074.

In operation with regard to the “or” circuit 2036, a sample A is drawninto the flow channel 2050 through inlet 2040 while a sample B is drawninto the flow channel 2052 through inlet 2042. Either the sample A orthe sample B, but not both sample A and B is deflected from the flowchannels 2050 or 2052 into the center channel 2054. Other means such asa microvalve or electromechanical switch may be employed to control theflow of ions from either channel 2050 or 2052 into the center flowchannel 2054. The deflected sample A or B is then delivered through theoutlet 2056 to a target such as the ionization or mixing region of apre-separation system.

In operation with regard to the “and” circuit 2038, a sample C is drawninto the flow channel 2068 through inlet 2058 while a sample D is drawninto the flow channel 2070 through inlet 2060. In this case both thesample C and D are deflected from the flow channels 2068 or 2070 intothe center channel 2072. The deflected samples C and D are thendelivered through the outlet 2074 to a target such as the ionization ormixing region of a pre-separation system.

The logic circuit 2034 may deliver multiple combinations of samplereactant ions such as the sample combinations A only, B only, ACD, andBCD. Other combinations of reactant ions may be enabled dependent on theconfiguration of the logic circuit 2034 array. For instance, logiccircuit may be arranged in parallel, in series, or in a combination ofseries and parallel in order to achieve a desired mixture. Although onlytwo circuits are shown in FIG. 64, the number and types of circuits maybe increased to facilitate the delivery of numerous combinations ofreactant ions to a target.

In certain illustrative embodiments, arrays of analyzers may be employedfor detecting and characterizing various compounds within a samplematrix.

FIG. 65 is a conceptual diagram of a sample pre-separation and analysissystem 2076 using multiple ionization zones and multiple analyzers toanalyze various ions of a sample matrix according to an illustrativeembodiment of the invention. The pre-separation and analysis system 2076includes sample inlet 2078, gas flow channel 2080, ionization region2082, ionization region 2084, ionization region 2086, analyzer 2088,analyzer 2090, analyzer 2092, and outlet 2094.

In operation, a sample matrix S is drawn into the gas flow channel 2080through inlet 2078 and then ionized in ionization region 2082. Due tocompetitive ionization, certain compound molecules are ionized intoproduct ions that are then extracted from gas flow channel 2080 usingany of the various techniques described previously. The extracted ionsare then analyzed by an analyzer 2088 such as a DMS, IMS, MS and likesystem.

The remaining neutral molecules of sample matrix S are then ionized inionization region 2084. Again, the product ions are extracted andanalyzed by an analyzer 2090. The remaining neutral molecules of samplematrix S are then ionized in ionization region 2086. The product ionsare extracted and analyzed by an analyzer 2092. Any remaining neutralmolecules exit the gas flow channel 2080 through outlet 2094. Anadditional analyzer may be employed at the outlet 2094 for furtheranalysis of the sample matrix S. The number of analyzers and ionizationregions may be varied depending on the number of product ions to beanalyzed.

FIG. 66 is a conceptual diagram of a sample pre-separation and analysissystem 2096 using multiple ionization zones and DMS analyzers, includinga DMS analyzer 2116 with an arbitrarily curved drift tube and ion filterregion 2122, according to an illustrative embodiment of the invention.The pre-separation and analysis system 2096 includes sample inlet 2098,gas flow channel 2100, ionization region 2102, ionization region 2104,ionization region 2106, DMS analyzer 2116 with a curved drift tube andion filter region 2122, analyzer 2118, analyzer 2120, deflector 2110,deflector 2112, deflector 2114, and outlet 2124.

In operation, a sample matrix S is drawn into the gas flow channel 2100through inlet 2098 and then ionized in ionization region 2102. Due tocompetitive ionization, certain compound molecules are ionized intoproduct ions that are then deflected from gas flow channel 2100 bydeflector 2110 into DMS analyzer 2116. The extracted ions are thenanalyzed by the DMS analyzer 2116. The DMS analyzer 2116 may include aarbitrarily curved drift tube and ion filter 2122 so that the electricfield in the DMS is non-uniform.

A portion of the remaining neutral molecules of sample matrix S are thenionized in ionization region 2104. The product ions are deflected bydeflector 2112 from the gas flow channel 2100 into the analyzer 2118 andanalyzed. The remaining neutral molecules of sample matrix S are thenionized in ionization region 2108. The product ions are deflected bydeflector 2114 into the analyzer 2120 and analyzed. Any remainingneutral molecules exit the gas flow channel 2100 through the outlet2124. An additional analyzer may be employed at the outlet 2124 forfurther analysis of the sample matrix S. The number of analyzers andionization regions may be varied depending on the number of product ionsto be analyzed. Also, the spacing between the ionization regions andanalyzers may not be uniform. Furthermore, while not shown in FIGS. 65and 66, multiple flow channels, each with one or more analyzers, may bearranged in parallel. In yet a further configuration, multiple analyzersmay be employed in series or parallel after each ionization region toenhance sample analysis.

FIG. 67 is a conceptual diagram of a sample pre-separation and analysissystem 2126 employing multiple ionization zones and analyzers along witha filtered gas source to control pressure within the analyzers accordingto an illustrative embodiment of the invention. The pre-separation andanalysis system 2126 includes a sample inlet 2128, gas flow channel2130, ionization region 2132, ionization region 2134, ionization region2136, analyzer 2138, analyzer 2140, analyzer 2142, analyzer flow channel2139, analyzer flow channel 2141, analyzer flow channel 2143, pressurechannel 2144, pressure channel 2146, pressure channel 2148, deflector2150, deflector 2152, deflector 2154, ion attractors 2156, exit port2155, exit port 2157, exit port 2159, ion attractors 2158, ion attractor2160, outlet 2162, and gas flow channel 2164.

In operation, a sample matrix S is drawn into the gas flow channel 2130through inlet 2128 and then ionized in ionization region 2132. Due tocompetitive ionization, certain compound molecules are ionized into agroup of product ions that are then deflected from gas flow channel 2130by deflector 2150 and attracted by ion attractors 2156 through exit portand/or opening 2155 into the analyzer 2138. The gas flow channel 2164provides filtered and/or treated gas to the analyzer 2138 throughpressure channel 2144 to establish a relatively higher pressure withinthe analyzer 2138. The relatively higher and/or positive pressure withinthe analyzer 2138 and analyzer flow channel 2139 limits the entry ofneutral molecules into the analyzer 2138. The extracted product ions arethen analyzed by the analyzer 2138.

The remaining neutral molecules of sample matrix S are then ionized inionization region 2134. The product ions are deflected by deflector 2152and attracted by ion attractors 2158 from the gas flow channel 2130through exit port 2157 into the analyzer 2140 and analyzed. The gas flowchannel 2164 provides filtered and/or treated gas to the analyzer 2140through pressure channel 2146 to establish a relatively higher pressurewithin the analyzer 2140. The relatively higher and/or positive pressurewithin the analyzer 2140 and analyzer flow channel 2141 inhibits and/orlimits the entry of neutral molecules from gas flow channel 2130 intothe analyzer 2140.

The remaining neutral molecules of sample matrix S are then ionized inionization region 2136. The product ions are deflected by deflector 2154and attracted by ion attractors 2160 through exit port 2159 into theanalyzer 2142 and analyzed. The gas flow channel 2164 provides filteredand/or treated gas to the analyzer 2142 through pressure channel 2148 toestablish a relatively higher pressure within the analyzer 2142. Therelatively higher and/or relatively positive pressure within theanalyzer 2142 and analyzer flow channel 2143 inhibits and/or limits theentry of neutral molecules from the gas flow channel 2130 into theanalyzer 2142.

Any remaining group of neutral molecules exit the gas flow channel 2130through the outlet 2162. An additional analyzer may be employed at theoutlet 2164 for further analysis of the sample matrix S. The number ofanalyzers and ionization regions may be varied depending on the numberof product ions to be analyzed. Furthermore, the spacing between theionization regions and analyzers may be non-uniform.

FIG. 68 is a flow diagram of a process showing the analysis of a samplematrix including re-circulation of the sample according to anillustrative embodiment of the invention. First, a sample matrix ismixed with reactant ions (Step 2166). Then, the reaction conditions arecontrolled to optimize the transfer of charge and ion species formation(Step 2168). Once the sample matrix is ionized to form product ions, theproduct ions are separated from the sample matrix (Step 2170). Ifdesired, the separated product ions may be analyzed (Step 2172). Next,it is determined whether all desired ion species of the sample matrixhave been removed (Step 2174). If all of the desired or selected ionspecies have been removed, the remaining neutral molecules of the samplematrix may be analyzed (Step 2178). If all of the desired ion specieshave not been removed, the remaining neutral molecules of the samplematrix are mixed with the reactant ions and the process is repeated(Step 2176).

FIG. 69 is a flow diagram of a process showing the analysis of a samplematrix composed of multiple molecule species according to anillustrative embodiment of the invention. First, the reactant ions areproduced (Step 2180). Then, a sample matrix is mixed with the reactantions (Step 2182). The reaction conditions are controlled to optimize thetransfer of charge and permit target ion species formation (Step 2184).Once ionized, the product or target ions are separated from the samplematrix (Step 2186). If desired, the separated product ions may beanalyzed (Step 2190). Then, the remaining neutral molecules of thesample matrix are mixed with the reactant ions (2192). Next, it isdetermined whether all desired ion species of the sample matrix havebeen removed (Step 2194). If all of the desired or selected ion specieshave been removed, the remaining neutral molecules of the sample matrixmay be analyzed (Step 2196). If not all of the desired ion species havebeen removed, the process is repeated.

FIG. 70 is a conceptual diagram of a sample pre-separation (neutralsremoval) system 2167 where the neutral molecules are removed from theionized molecules rather than removing the ions from the neutral gasstream as described previously. The sample pre-separation system 2167includes sample inlet 2169, clean gas inlet 2171, clean makeup gas inlet2173, clean makeup gas inlet 2175, optional ionization source 2177, gasflow channel 2179, electrodes 2181, flow permitting medium 2183, neutralremoval region 2185, analyzer 2187, and neutrals flow outlet 2189.

In operation, a sample matrix S is drawn into the pre-separation devicethrough sample inlet 2169 and ionized by reactant ions. The ions aretransported by an electric field, generated by electrodes 2181, towardsan analyzer 2187 while sample S neutrals are drawn away from the sampleions through a “flow permitting” medium 2183. The flow permitting medium2183 may include a porous material or a region with small openingsand/or holes to allow the neutrals to pass from the gas flow channel2179 through the neutrals flow outlet 2189. The sample S neutrals maythen be removed from the sample S ions in the neutral removal region2185 using a vacuum pump that creates a vacuum in the neutral removalregion 2185. The vacuum draws the neutrals out of the gas flow channel2179, e.g., a transport tube, while the ions are moved towards theanalyzer 2187 by the electric fields of the electrodes 2181.

The ions may move in direction 2191 counter to a clean gas flow-makeupstream which is free of sample neutrals. A gas flow-makeup stream mayoriginate from a clean makeup gas inlet 2173 and/or clean makeup gasinlet 2175. The sample pre-separation system 2167 may use discreteelectrodes 2181, or resistive ink or semi-conducting coatings withsuitable voltages and currents applied to induce the desired electricfields. The gas flow channel 2179 may be enclosed substantially by asubstantially circular and/or rectangular housing. With a substantiallycircular housing, the electrodes 2181 may be circular rings along thegas flow channel 2179. With a substantially rectangular housing, theelectrodes 2181 may reside on opposing facing planar surfaces with thegas flow channel 2179 in between. The sample pre-separation system 2167may be planar in form.

The sample pre-separation (neutrals removal) system 2167 may interfacewith a DMS or IMS or MS or the like. In the illustrative embodiment ofFIG. 70, the sample S may be mixed with reactant ions that areoptionally introduced at inlet 2171 and ionized by ionization source2177. The mixture is transported into the separation region 2185 whereproduct ions and some reactant ions are separated from the sampleneutrals and transported to an analyzer 2187. Alternatively, pre-ionizedsample S molecules may be introduced into the gas flow channel 2179 atinlet 2169. The separation, or neutral removal, region 2185 may then usea clean gas flow in the direction 2193, which is transverse to the ionflow, to draw the neutral sample S molecules away from the ions in thegas flow channel 2179. The remaining sample S molecules are thendelivered to the analyzer 2187 for analysis.

FIG. 71 is a conceptual diagram of a sample pre-separation system 2198employing an ionization region 2200, ionization source inlet 2202,analyzer flow channel 2221, DMS ion filter 2204, deflector 2206, ionattractors 2208, exhaust opening 2210, neutral molecules 2212, pump2214, and valve 2216 to selectively filter ion species for analysisaccording to an illustrative embodiment of the invention. In operation,a sample matrix S is drawn through valve 2216 when the valve 2216 ispositioned to accept the sample matrix S. The valve 2216 mayalternatively be positioned to only allow neutral molecules 2212 tore-circulate to the DMS inlet 2218 and ionization region 2200. Anionization inlet 2202 may be employed to enable the introduction ofreactant ions. The reactant ions may then mix with the sample matrix Sand ionize selected compound molecules.

The DMS ion filter 2204 and an optional detector electrode 2220 mayremain inactive until a sufficient amount of pre-separation iterationsare performed to remove unwanted ion species from the sample matrix S.Once the sample matrix S is ionized, the deflector 2206 and ionattractors 2208 propel the product ions from the analyzer flow channel2221 through the opening 2210. These product ions may be furtheranalyzed or discarded.

The remaining neutral molecules 2212 of the sample matrix are thenpropelled by the pump 2214 through the valve 2216 back to the DMS inlet2218. The remaining neutral molecules 2212 may be re-circulated until adesired type of compound remains. Then, the DMS filter 2204 and detector2220 may be activated to analyze the remaining compound of the samplematrix S. Alternatively, the deflector 2206 and/or ion attractors 2208may function as detector during the DMS analysis.

FIG. 72 is a conceptual diagram of a sample pre-separation system 2222employing an ionization region 2224, ion guiding region 2226, DMS ionfilter 2228, positive electrodes 2230, negative electrodes 2232,optional analyzers 2234, flow generator 2242, selective concentrator2244 and valve 2248 for ion species analysis according to anillustrative embodiment of the invention. The pre-separation system 2222also includes DMS inlet 2250, DMS flow channel 2240, DMS outlet 2252,flow generator 2242, opening 2236, and opening 2238.

In operation, a sample matrix S is drawn through the valve 2248 and theDMS inlet 2250 into the ionization region 2224. The sample matrix S isthen ionized using one of the various ionization techniques previouslydescribed. Due to competitive ionization, certain compound molecules areionized into product ions. The ion guiding region 2226 then concentratesthe ions to the center of the DMS flow channel 2240. The DMS ion filter2228 may be activated at certain times to perform ion filtering. Then,the product ions are deflected from the DMS flow channel 2240 by eitherpositive electrodes 2230 or negative electrodes 2232. The positiveelectrodes 2230 act simultaneous as an attractor for negative productions and as a deflector for positive product ions. Also, the negativeelectrodes 2232 act simultaneous as an attractor for positive productions and as a deflector for negative product ions. Thus, both positiveand negative product ions may be removed from the DMS flow channel 2240simultaneously or at about the same time.

The remaining neutral molecules of the sample matrix S pass through theDMS outlet 2252 to the flow generator 2242. The flow generator 2242establishes gas flow in the DMS flow channel 2240 from the DMS inlet2250 toward the DMS outlet 2252. The flow generator 2242 may be asolid-state or electromechanical pump or the like. The flow generator2242 then propels the neutral molecules through the selectiveconcentrator 2244 which further concentrate the sample matrix S byremoving unwanted compounds. The concentrator controller 2246 mayregulate the conditions within the concentrator to enable sample matrixS concentration.

The remaining concentrated and neutral molecules of the sample matrix Sthen pass through the valve 2248 and return to the DMS inlet 2250 forfurther pre-separation if necessary. The valve 2248 may be positioned toallow an external sample matrix S to be collected, positioned tore-circulate only the neutral molecules, or positioned to allow both theexternal sample matrix S intake and re-circulation of the neutralmolecules.

The previous pre-separation systems may be improved by use of molecularsieves, membranes, and the like, such as those described supra. Forexample, a membrane may be employed at various openings to maintain thepressure and re-circulated gas flow in a pre-separation system whileallowing product ions to be removed. Also spectral changes may bemonitored during the pre-separation process to provide an indicationwhen adequate cleaning of a gas sample reached or when a particularcompound may be sampled.

While current mobility based analyzers are sensitive, there is a need todetect concentrations in ranges lower than parts-per-trillion (ppt). Forinstance, a very small number of anthrax spores may cause significanthealth effects. However, existing analyzers may not be sensitive enoughto detect the charge generated by such a small number of spores. Onetechnique for overcoming this limitation is concentrating and/oramplifying the number of molecules of a sample, in time, to enable ananalyzer to produce a larger signal for detection.

In certain embodiments of the invention, chemical amplification isemployed to enable the detection of extremely low levels (e.g.,concentrations of less than a few ppt) of analytes in a sample. Thesample may be a fluid such as a vapor or liquid. By allowing selectedmolecules to circulate multiple times in an analyzer system, theconcentration of an analyte may be increased to a detectable level.

FIG. 73A is a conceptual diagram of a sample amplification system 2254employing a DMS filter 2256, detector and neutralizer 2258, transportgas input 2260 and re-circulation loop 2262 for selected ion speciesanalysis according to an illustrative embodiment of the invention. Inoperation, a sample S is drawn into the DMS filter 2256 which filtersout and exhausts unwanted ion species. The selected ion species aredelivered to the detector and neutralizer 2258, which detects andneutralizes the selected ion species during the detection process. Atransport effluent (e.g., a gas, liquid or vapor) input 2260 providestransport effluent (in the example a transport gas) to flow theneutralized ion species through the re-circulation loop 2262. Uponreturn to the DMS filter 2256, the neutralized ion species are mixedwith more sample S molecules and then filtered by the DMS filter 2256.The sample amplification process is repeated for a period of time untilenough of the selected ion species are filtered by the DMS filter 2256for the detector and neutralizer 2258 to detect the ion species ofinterest.

FIG. 73B is a conceptual diagram of a sample amplification system 2264employing a DMS filter 2266, detector 2268, ionization source 2270,deflector 2272, an attractor grid 2274, DMS flow channel 2276,re-circulation channel 2278, inlet 2280, exhaust 2282, and an optionalDMS 2284 for analysis of selected ion species according to anillustrative embodiment of the invention.

In operation, a sample S is drawn into the DMS flow channel 2276 throughthe inlet 2280. The DMS filter 2266 filters out unwanted ion specieswhile the detector electrodes 2268 detect the ion species of interest.Because the detected ions may be neutralized during detection, theionization source 2270 then ionizes the sample S, including theneutralized ions. After ionization, the deflector 2272 propels theproduct ions through the attractor grid 2274 into the re-circulationchannel 2278. The unwanted and filtered compounds are exhausted from theDMS flow channel 2276 through exhaust 2282.

The product ions may optionally be analyzed by analyzer 2284 beforebeing circulated through re-circulation channel 2278 to inlet 2280 formixing with more sample S molecules. Then, the mixture is circulatedthrough the sample amplification system 2264 for another stage offiltering and detection. At the completion of each iteration offiltering and detection, the concentration of the target or desired ionspecies increases until the detector electrodes 2268 are able to detectthe target species of interest.

FIG. 74 is a conceptual diagram of a sample amplification and analysissystem 2286 employing a re-circulation channel according to anillustrative embodiment of the invention. The sample amplification andanalysis system 2286 includes a inlet 2288, ionization region 2290,ionization source inlet 2292, DMS filter region 2294, deflection plate2296, guiding electrodes 2298, detector and neutralizer electrode 2300,exhaust 2302, opening 2304, transport gas inlet 2306, re-circulationchannel 2308, and DMS flow channel 2310.

In operation, a sample S is drawn into the DMS flow channel 2294 throughthe inlet 2288. The sample S is ionized in the ionization region 2290.The ionization source inlet 2292 enables the injection of reactant ionsinto the ionization region 2290. Alternatively, an ionization source mayreside within the ionization regions such as a plasma generator, UVsource, or radioactive source. Once ionized, the sample is filtered inthe DMS filter region 2294 to allow only a desired or selected ionspecies to reach the deflector 2296. The unwanted, filtered, andneutralized ion species travel through the DMS flow channel 2310 and arediscarded through the exhaust 2302.

The selected ion species, however, are deflected by the deflector 2296through the opening 2304 into the re-circulation channel 2308. Theguiding electrodes 2298 guide the selected ion species through theopening 2304 and toward the detector and neutralizer electrode 2300.Once the selected ion species are detected and neutralized by electrode2300, transport gas from transport gas inlet 2306 propels theneutralized ions through the re-circulation channel 2308 toward theionization region 2292. In the ionization region 2292, the neutralizedions are mixed with new sample molecules and ionized. The new mixture isthen circulated through the amplification and analysis system 2286 andso on over a period of time until the concentration of the selected ionspecies reaches level that can be detected.

FIG. 75 is a flow diagram of a process of amplification of a selectedion species using an analyzer such as a DMS. First, a sample iscollected and introduced (Step 2312). The sample is then passed througha DMS filter (Step 2314). The DMS filter may be controlled fordesignated time period to allow only a desired ion species to passthrough the filter region without being neutralized (Step 2316). Thecompounds that are neutralized and/or not ionized are ejected from theDMS filter and analyzer (Step 2318).

Next, the remaining filtered ions are collected and neutralized (Step2320). The neutralized ions are then mixed with additional samplemolecules and/or a transport gas (Step 2322). The mixture is passedthrough the DMS filter for second stage of analysis (Step 2324). Theprocess is repeated until a sufficient concentration of the desired ionspecies or compound is present for detection and analysis (Step 2326).

Although the invention has been described with regard to particularillustrative embodiments, it should be appreciated that the invention isbroader in scope and can be applied to any system for identification ofunknown species of ions traveling through a varying controlledexcitation field, the identification being based on the knowncharacteristic travel behavior of the species under the varying fieldconditions. The ion or ions to be identified may be traveling alone orin a group of ions of same or differing characteristic travel behavior.Additionally, the ion or ions to be identified may be transportedthrough the systems and devices of the invention by any suitableeffluent, including transport gasses, liquids and/or vapors. The filterfield may be compensated in any of various manners as long as a speciesof interest is returned to the center of the flow and permitted to passthrough the filter while all other species are retarded or neutralized.Identification is made based on known field-dependent differentialmobility behavior of at least one species of ions traveling in the fieldat known field conditions.

It should also be appreciated that in various practices, the inventionprovides improved systems, methods and devices for ion speciesidentification. According to some features, the invention varies one ormore filter field/flow channel conditions to improve speciesdiscrimination. For example, according to some illustrative embodiments,the invention determines changes in ion mobility, based, for example, onchanges in: Vrf; Vcomp; field strength; Vrf duty cycle; Vrf wavelength;Vrf frequency; and/or flow channel temperature, pressure, humidity, flowrate, doping and/or carrier gas CG composition. According to otherfeatures, the invention takes multiple scans of the sample S, forexample, by recirculating the sample S and/or processing the sample S inparallel and/or in series with one or more additional DMS, IMS, TOFIMS,GC, FTIR, MS, or LCMS, at differing flow channel/filter fieldconditions.

According to further features, the invention employs approaches, suchas, fragmenting, lowering pressure, three-dimensional dispersionplotting, ion pre-separation, and/or ion amplification to enhancedetection resolution. According to other features, the invention storesa library of signatures for known compounds and pattern matches datafrom unknown compounds with the stored library to identify the unknowncompounds. It should be understood that the invention is applicable notonly to planar DMS systems, but may be applied in general to ionmobility spectrometry devices of various types, including variousgeometries, ionization arrangements, detector arrangements, and thelike, and brings new uses and improved results even as to structuresthat are all well known in the art.

Thus, the invention is not limited to configurations of the illustrativeembodiments and may be practiced in any other suitable configurations,including radial and cylindrical DMS devices. Additionally, variousmodifications and variations may be made to the invention withoutdeparting from the spirit and scope herein.

1. A sample analysis system, comprising: an ionization source forionizing a sample; an ion mobility filter including, at least two filterelectrodes, and an ion flow path between the at least two filterelectrodes, wherein the pressure in the ion flow path is between about0.2 to 0.9 atmospheres; a controller operatively coupled to the ionfilter for controlling operation thereto; and an ion detector forsensing ions not filtered by the ion filter.
 2. The system of claim 1,wherein the pressure in the ion flow path is between about 0.2 to 0.7atmospheres.
 3. The system of claim 2, wherein the pressure in the ionflow path is between about 0.2 to 0.6 atmospheres.
 4. The system ofclaim 3, wherein the pressure in the ion flow path is between about 0.2to 0.5 atmospheres.
 5. The system of claim 4, wherein the pressure inthe ion flow path is between about 0.2 to 0.4 atmospheres.
 6. The systemof claim 5, wherein the pressure in the ion flow path is between about0.2 to 0.3 atmospheres.
 7. The system of claim 1, wherein the at leasttwo filter electrodes are planar electrodes.
 8. The system of claim 1,wherein the ion mobility filter is a differential ion mobility filter.9. The system of claim 1, wherein the ion detector is a massspectrometer.
 10. The system of claim 1, further comprising a gaschromatograph connected to the ion mobility filter.
 11. A method foranalyzing a sample, comprising: ionizing the sample using an ionizationsource to produce a first group of ions; filtering the first group ofions using an ion mobility filter to produce a second group of ions,wherein the pressure in the ion mobility filter is between about 0.2 to0.9 atmospheres; sensing ions in the second group of ions using an iondetector.
 12. The method of claim 11, wherein filtering the first groupof ions includes applying an asymmetric electric field to the firstgroup of ions.
 13. The method of claim 12, wherein the pressure withinthe ion mobility filter is varied during filtering.
 14. The method ofclaim 13, wherein a constant ratio of the electric field strength to thepressure is maintained as the pressure is varied.
 15. The method ofclaim 12, wherein sensing ions includes sensing ions in positive iondetection mode.
 16. The method of claim 12, wherein sensing ionsincludes sensing ions in negative ion detection mode.
 17. The method ofclaim 12, further comprising processing, using a processor, informationfrom the ion detector to perform the analysis of the sample.